Running short of worries? Then ponder the super-volcanoes — earth-bombs that can vomit 10 or 100 or 1,000 cubic kilometers of molten rock. Super-volcanoes can change history by creating rivers of red-hot ash moving at highway speed, spreading dust across hundreds of kilometers and spewing vapors that block the sun, destroy crops and start famines.

A volcano may go dormant for thousands of years after such a huge eruption, so they may be even harder to predict than smaller ones — which are also unpredictable at this point…

But this week, Nature published a new analysis of Santorini, a Mediterranean monster, that shows the movement of molten rock that preceded the eruption.

Santorini’s sudden release of 40 to 60 cubic kilometers of rock and ash was followed by a giant collapse that left a characteristic ring of hills called a caldera. Thousands may have died in the eruption, which laid down a 60-meter layer of ash and rock.

Eruptions of this general size happen about every 300 years, says Timothy Druitt, a volcanologist at the Université Blaise Pascal in France, who lead the current study. The most recent was in 1815 at Tambora, in Indonesia.

Druitt’s new analysis of crystals within the frozen magma offers a rough schedule for the entry of molten magma into a holding tank — the magma chamber — below the volcano, which is a precursor to eruption.

Caldera-forming eruptions rival earthquakes and tsunamis as the deadliest natural disasters. “People who work in the field know these volcanoes are not rare, even on a human time scale,” says Druitt, but “we have never been able to monitor one of these big eruptions during the long buildup phase, so we are not really sure how that happens.”

The crystal analysis detects microscopic changes in chemical composition, offering a unique, after-the-fact picture of the gestation of eruption.

In the crystals

As crystals grow in the cooling magma, atoms of trace elements diffuse within them, and both growth and diffusion are affected by conditions within the hot magma, says Druitt. “These crystals grow progressively, and as they do, their chemical composition changes according to the composition of the magma around them, and the temperature and amount of water in the magma.”

The crystals revealed that a big gob of magma — perhaps 10 percent of the magma chamber’s total contents — entered in the decades before the eruption. “Looking at the crystals in this magma, we were able to reconstruct very crudely events taking place in the last few decades prior to the eruption,” Druitt says.

That final addition probably made the magma chamber unstable, leading to the eruption, Druitt explains.

If such a late, large magma movement proves typical of super-volcanoes, that could contribute to a distant early warning system for mega-eruptions, based on more conventional methods, such as seismic monitoring.

Distant early warning

But the findings also carried a caution, Druitt says, since Santorini was apparently dormant for about 18,000 years before the last apoplectic outburst. “That is a slightly alarming result. There are lot of these big caldera systems, but most are in a stage of repose.”

The upshot is more proof that a dormant volcano can still be a dangerous one, he adds. “We can imagine that a big caldera in a remote region of the world, such as the Andes, which is not monitored very well, could reawaken pretty quickly on a human time scale.”

The crystal method gives after-the-fact data on an eruption. Current attempts to anticipate eruptions rely on data about earth shaking, deformation of the crust, and release of gases.

“It’s a very timely topic, and solid science in terms of the measurements and observations,” says Bradley Singer, a volcanologist and professor of geoscience at University of Wisconsin-Madison. “They admit that there are issues about the time scales,” largely because the diffusion of strontium and titanium is imperfectly understood in the hot magma.

The study’s title, however, specifies that the final growth of the magma chamber occurs on “Decadal to monthly timescales,” Singer notes. “It could be centuries or even longer, which implies that we’d have a longer time prior to the eruption” to worry about the effects of the rising magma.

Singer concurs on the importance of understanding the relationship of magma flows, instability and eruption, and says the crystal analysis is gaining traction in volcanology.

That’s just as well, since giant caldera-forming volcanoes may be frighteningly common. The one at Yellowstone, for example, released 1,000 cubic kilometers of rock 640,000 years ago. Wouldn’t you want to know if something like that was building on your continent?

Interested in waterfront property in Southern California? A new study of a continental schism running east of Los Angeles offers a clear “buy” signal for the long-term investor: The North American continent is splitting apart along a rift, and if you got the patience, we have the real-estate-appreciation potential!

In just a few million years, as the North American continent sunders in a weak zone called the Salton Trough, the Gulf of California will stretch further north.

On our unstable Earth, not even the continents are rock solid. Instead, they shift around like blocks of sea ice that join, fissure and separate once again — over millions of years.

Geologists know the process is occurring in the Southern California desert, and we’ve just read a sophisticated analysis that finds an ominous thinning of the strong crustal layer in the Salton Trough.

Ominous, that is, unless you are planning a waterfront resort here, with a grand opening in, say, 2,002,011.

The study helps to fill a gap in our understanding of the earth, says first author Vedran Lekic, a National Science Foundation post-doctoral fellow at Brown University. “The main question is, how do continents come to break apart? This process is really fundamental to shaping how the Earth looks; if not for rifting, once Pangaea formed, it would never have broken apart and we would have only one continent.”

Pangaea is a giant agglomeration of continents that broke up about 150 million years ago, creating our current collection of continents.

Scoping out the Earth

The lithosphere, Earth’s crust and the rigid rock beneath it, essentially floats on the asthenosphere, the soft and hot outer layer of the mantle that is located tens of kilometers belowground.

As a continental rift grows, one would expect to find a thinned lithosphere at the Salton Trough. But Lekic says the actual thinning was more dramatic than expected — as much as a 50 percent reduction compared to adjacent areas.

By studying earthquake waves passing through Earth, Lekic and colleagues measured the thickness of the lithosphere by locating its lower border. They knew that one type of wave converts to a faster wave type as it passes up from the asthenosphere into the lithosphere, so the conversion could be used to mark the base of the lithosphere.

It turned out that the lithosphere measured about 40 kilometers thick beneath the Salton Trough, compared to 60 to 80 kilometers on nearby areas. That thinning translates into a weakening that will eventually allow open water into the Trough, and myriad real-estate opportunities along the new shoreline.

Previous efforts to estimate the lithosphere’s depth have relied mainly on surface data, says Lekic, and that limited our knowledge of how the continental splitsville takes place. From relying on “surface observations of faults, topography, heat flow, and some studies of the crustal structure, we have not been able to image the detailed topography of the base of the tectonic plate, as it looks during rifting.”

Rift terrific

Although the study relied on the interest in Southern California seismology that is a response to extreme seismic activity, the finding says little about earthquake probabilities.

But earthquakes are not the only tectonic game in town, says Eugene Humphreys, a professor of geophysics at the University of Oregon. “While most people know southern California is being sheared by the San Andreas and related faults, most people are not aware that the region also is being pulled apart as the Pacific plate also moves slowly away from North America. These researchers have imaged the deep structure of the plate where it is being torn apart by this process, and contrary to what many have thought, the tears go through the entire plate right where the surface expression of this rifting is seen. It’s exciting work.”

The study provides insight into deep structure and processes of fluid migration up into the plate, says Humphreys. “These lower-plate interfaces were not expected to exist at all, and the scientific community is excited but struggling to determine what could create relatively sharp interfaces.”

Although Earth warms with depth, that is unlikely to explain the weakness, Humphreys says, “so the search for other causes is on. By associating the position and shape of these interfaces with a specific deformation history, this study provides important information on the origin of these interfaces.”

Lekic, who worked with co-author Karen Fischer of Brown, on the study, says that “Even at great depth, we see the same stretching and deformation that we see near the surface. At the bottom of the lithosphere, there is this persistent weakness, in a zone that runs more or less vertically, and that’s surprising.”

But as scientists wrestle with the geological goulash that is Southern California, we suggest you send a down payment to Rift ‘n Grift Realty on the ocean-front lot of your dreams – and wait a few million years!

— David J. Tenenbaum

Uganda is looking for answers as about 20 students and a teacher were killed June 28 by lightning that struck their school in this highland nation in Eastern Africa. With dozens of children also injured by electricity, Ugandans wonder if the serious string of lightning strikes is related to climate changes, or are just the consequence of an unusually heavy stream of moist air coming from the Atlantic.

We can’t answer, but the tragedy did get us Why Filers to thinking about lightning. Although lightning bolts killed “only” an average of 39 Americans over a recent 10-year stretch, the injuries, which concentrate on the vulnerable nervous system, can be severe and lifelong.

Satellites tell us that 1.2 billion lightning flashes occur in the atmosphere each year — although not all reach Earth.

What is lightning? How does it injure and kill? And what has been learned in the past few years from the millions spent studying nature’s electricity?

2003, NASA Johnson Space Center

A string of lightning flashes are seen from space.

Boom-boom room

Thunder — the cracking or rumbling you often hear — is caused by thermal expansion and contraction. Lightning bolts can get far hotter than the sun’s surface — up to 20,000° Celsius. That heats the air, causing it to expand, and starting a shock wave that moves as sound waves — thunder.

If you’re close to the lightning bolt, you’ll hear a cracking; further away, you’ll hear rumbling because that sound has come from several parts of the bolt, and been reflected from buildings and hills.

And yes, if you start counting “one Mississippi,” when you see the flash, you can estimate the distance to the bolt: Light essentially reaches you instantly, but sound takes about five seconds to travel one mile. Divide the number of seconds by five to find miles, or by three for kilometers.

Silence is — mysterious

One of the many lightning mysteries is this: Sometimes you hear the thunder, and sometimes you don’t. For example, “heat lightning” is an eerie, silent flash that often lights clouds in thunderstorms.

The sound has been gobbled by an audio version of the visual mirages that cause trekkers to see water in stone-dry desert. These visual mirages are caused by heat that bends light waves. You look straight ahead, but you actually see the sky, shimmering like a tempting lake.

Similarly, in a thunderstorm, the sharp boundaries between warm and cool air can channel sound waves away from the observer, as you can see from the nifty applet, below.

Much the same phenomenon was noticed during the Civil War, when artillery was visible in the distance but audible only in some parts of the battlefield.

Go play with lightning.

Nature’s lighting foundry

We think of clouds as billowy places, couches for angels in Renaissance paintings. In thunderclouds, however, air and water – liquid, frozen and in between — may be whizzing up and down at a furious clip — up to 100 miles an hour.

That’s a place where angels fear to tread.

The motion in these cumulonimbus clouds is powered by convection, a force that separates fluids based on density. The dense, cold air falls while the warmer air rises. Smaller water droplets hitchhike up on the updrafts, which can’t support the larger droplets.

Because smaller particles tend to carry positive charges, the movement caused by temperature, humidity and density (which can include snow, ice, and water vapor) segregates electrical charges: The top of a cloud becomes positive and the bottom negative.

Regions of different charge can only exist if surrounded by an insulator — namely air. Insulators, however, eventually fail when they are overwhelmed by electric “pressure.” In a thunderstorm, that “failure” results in lightning.

Hangin’-motor blues

Having trouble envisioning this? Imagine a chain holding a greasy V-8 motor above a ’63 Ford Fairlane in a shade-tree auto mechanic’s backyard. If the engine is too heavy, or the chain too weak, the chain will snap as it is overwhelmed by the gravitational attraction between Earth and engine.

Thunk!

Substitute air’s insulation for the chain, and electrical attraction between positive and negative charges for gravity, and you have a greasy-fingered picture of how air can separate electrical charges during a thunderstorm.

To go further, we need one hunk of physical-science jargon: electrical potential is how fast charge changes with distance, and it’s measured in volts per meter. Electrical potential is the “pressure” that’s “trying” to start an electric current between areas of opposite charge.

(Opposite electrical charges are like young lovers: They will do anything to get together.)

Just as an overweight V-8 can snap a skimpy chain, excess electrical potential can “break” air’s insulation. When that happens, an electrical current — in the form of a lightning bolt — neutralizes the opposing charges.

Flash!

Diagram: Encyclopædia Britannica, Inc.

Lightning leaps between separate negative and positive regions during a storm. Most cloud-to-ground flashes originate in the cloud’s negative regions.

In a cloud-to-ground flash, the huge electrical potential — measured in millions of volts — eventually overcomes air’s electrical resistance, and a “streamer” or “leader” begins reaching, about 50 meters at a time, toward ground. The streamer makes an ionized (conducting) pathway of plasma, allowing current to flow.

Where am I safe?

As the current approaches the ground, its electrical potential can cause a surge of oppositely-charged particles to “reach” up toward it. Because this upward current often springs from tall objects, trees and other tall objects make lousy shelter during a storm.

For a 2001 Why File on lightning, David Rust, who was then director of forecast research and development at the National Severe Storms Laboratory, told us that the safety of a building is determined by the degree of grounding. A steel building that’s securely grounded, he said, will be safer than a wooden one that’s not, even if the steel building is taller. Steel and other conductive metals provide an easy pathway to ground for the lightning, and that translates into safety.

Once the ionized pathway is established, electric currents flow back and forth between ground and cloud so quickly that they appear as flickers rather than separate bolts. (More on lightning safety.)

We’ve heard that a big cloud-to-ground bolt carries one trillion watts of electricity. If that estimate is right, during its fraction-of-a-millisecond life, the flash carries about the same current as the total U.S. generating capability. (Watts measure the flow of electric current at any instant. The more familiar watt-hours measures an hour of flow of a given current; 1 kilowatt hour equals 1,000 watt hours.)

But nobody has figured out how to put this energy to work. Though we have heard one proposal, the currents are insanely high and the strikes are too brief and too unpredictable.

Keeping a close watch on lightning

Our understanding of lightning grows with improvements in technology, and a new instrument on trusty weather balloons has pointed to a surprising source for the electric charge. The process involves a small, spongy relative of hail called graupel, says Don MacGorman a physicist at NOAA’s National Severe Storms Laboratory.

“As graupel accumulates tiny, pristine ice particles, and then falls through liquid water, there can be some charge exchange in collisions where the tiny ice particles rebound,” MacGorman says. In the lab, this interaction seems powerful enough to be main source of electricity – and therefore lightning — in large areas of the storm.

Within a few years, a better understanding of lightning formation could improve predictions, MacGorman says. “We will not be able to say lightning will a hit particular location. Lightning is too random for that, but we are getting to the place where it may be possible to say that a storm will produce a little or lot of lightning, and that would be helpful for storm safety.”

Cloudy picture

The graupel explanation, however, raises a question: If the interaction of water and ice creates the electric charge, why is lightning found in dry sectors of the storm, including the large “anvil” structure that exhausts cold, dry air above the storm? “We have seen lightning initiated almost 100 kilometers from the heavy precipitation area, so something else must be going on in the anvil,” says MacGorman. “This does not accord with how we’d viewed anvils.”

Scientists are also probing cloud flashes, caused by the flow of current between regions of clouds with opposite charges and does not hit the ground. Formerly dissed because they don’t kill people, cloud flashes are getting some respect.

For one thing, they are the most common type of lightning, accounting for perhaps one-quarter of all lightning flashes. Adding cloud-to-ground and cloud-to-cloud lightning gives a better indicator of total storm intensity than ground flashes alone, “which have very little relationship to storm severity,” says MacGorman. “You can have huge ground flashes in a relatively innocuous storm, but total lightning is well related to things that affect severity and strength: the size of the updraft, the amount of ice in the clouds, and so it gives us clues as to how intense the storm is.”

Positively speaking

The biggest recent discovery on lightning, says MacGorman, concerns storms that produce a large amount of positively charged cloud-to-ground lightning rather than the usual negative currents. During a field research program called STEPS, in a lightning-rich region of the high plains, some storms contained negative charges in places that normally would be positive, and vice versa. In these conditions, instead of dropping the normal negative charge to the ground, the lightning bolts were positive.

The unusual phenomenon could arise in clouds containing a high concentration of liquid water, MacGorman says, and that would also raise the odds of large hail. “Hail typically forms because graupel or another seed particle starts collecting liquid water faster than it can freeze, and the water spreads over the surface, then freezes into a solid layer of ice.”

These dense particles are more likely to happen in an area with a lot of liquid water, and therefore, these positive lightning strikes could be a harbinger of large, destructive, hail.

The view from on high

For the next stage in lightning observations, scientists will go to GOES-R, a series of geostationary satellites scheduled for launch in 2015. These high-orbital spyglasses will carry an optical gadget that should “see” upwards of 90 percent of total lightning activity. “The viewing area will cover pretty much all of the continental United States, and parts of Africa and South America, and eventually, half of the Pacific Ocean,” says MacGorman. “This will allow us to detect thunderstorms over the oceans, which we have not had good way to see in the past.”

That should help airplanes dodge storms, but also aid weather prediction, MacGorman says, since thunderstorms can trigger other thunderstorms. They also add water vapor to the lower atmosphere, which also feeds storms.

Nothing light about lightning

Lightning gathers myths. Whether it’s Zeus throwing thunderbolts from the ancient Greek sky, or the moronic misconception that victims become untouchables because they retain an electric charge, these bolts spark the imagination.

But lightning can change your life, as Steven Marshburn, Sr., of Jacksonville, N.C., told us in 2001. Marshburn was struck in 1969 while working in a bank. Although the sky was blue and no storm was in sight, a bolt entered through a wire from the drive-up window.

Afterwards, Marshburn “suffered from severe headaches, chronic daily pain, grand mal [epileptic] seizures, dizziness, problems with my eyes going blurry. Many health problems persist. I have had 20 lightning-related surgeries…”

In 1989, in response to his brush with death, he formed Lightning Strike & Electric Shock Survivors International to investigate the medical aspects of lightning and to support victims and families. In 2001, he told us that members had talked 13 fellow survivors out of suicide.

A shock to the nervous system

Lightning usually kills by attacking the heart, which runs on electrical impulses. While high-voltage electrical injuries often cause severe burns, they are rare with lightning, likely because the bolts — lasting only 0.1 to 1 millisecond –- are too brief to cause severe burns.

Although burns may result if clothing ignites or sweat boils and steam is trapped under clothing, wet, sweaty clothing may actually conduct a heavy current outside the body and reduce the damage.

Raphael Lee, a professor of surgery and medicine at the University of Chicago, and an expert on the effects of lightning strike, told us that most of the initial current in a lightning strike does not pass through the body. However, two electromagnetic phenomena can produce a strong voltage drop across the body:

Strong electric fields are a problem for nerves and muscles, Lee says, because they “have been structured through evolution to be very sensitive to tiny electric fields.” That, combined with their physical length, which spans a large electrical gradient, “makes them very sensitive to lightning.”

Nerve cells can be a meter long, and by extending into different parts of an electric field, they are exposed to high voltages, Lee says. One focus of concern is the cell membrane which can die if strong voltages poke holes in it. Voltage can also wreak havoc in the pores in the membrane, which regulate the cell’s physiology by controlling how ions enter and leave the cell. Normally, for example, the potassium concentration is 1,000 times higher inside a cell, and damage to the pores can result in malfunction or cell death.

Lightning = thunder in the brain?

Although electricity is the natural focus of lightning damage, Lee suspects that an acoustic pulse, or shock wave, plays a major role, and perhaps a dominant one. A lightning bolt is surrounded by hot, ionized gas that arises in nanoseconds or microseconds and whose temperature may exceed 10,000 ° C. “When you heat something in a small area in such a short period, there are going to be shock waves,” he says.

The power of this acoustic wave is obvious when lightning hits and splits a tree, Lee adds. But inside the brain, the shock can trigger traumatic injuries similar to those caused by a roadside bomb or artillery shell.

Neurological injury: no passing matter

Lightning injury can be severe, long-lasting, and hard to treat, and it “may affect any or all parts of the nervous system,” according to Mary Ann Cooper, an emerita professor of emergency medicine at the University of Illinois-Chicago.

In a 2009 study of survivors of lightning and other electric shocks, 78 percent of the survivors had at least one psychiatric diagnosis; many of the troubles related to learning, memory and executive function.

In 2001, Cooper told The Why Files that confusion, caused by slowed information processing, is a hallmark of lightning injury. Symptoms include “difficulty in short-term memory, coding new information and accessing old information, multitasking, distractibility, irritability and personality change.”

Damage to the frontal lobe, the site of much higher thinking, is common, according to Cooper. “Many suffer personality changes because of frontal lobe damage and become quite irritable and easy to anger. The person who ‘wakes up’ after the injury often does not have the ability to express what is wrong with them…and cannot carry on a conversation, work at their previous job, or do the same activities that they used to handle. As a result, many self-isolate, withdrawing from church, friends, family and other activities.”

Cooper said some cell types continue suffering for weeks after the injury, and that nerve cells seem to “spend a long period trying to heal themselves, until finally the cell body is exhausted” and the cell dies. That process accounts for a delayed disability syndrome among survivors.

Help at hand?

Long-term neurological consequences are a major research area, Lee says, because they also occur in traumatic brain injury. “People are trying to sort out what is the best treatment, and understand why some people are more susceptible to delayed neurological problems. The body is very complicated and … the weight of evidence suggests there are genetic predispositions to complications after a blast causes traumatic injury to the brain, and lightning injury may be no different. Many people recover, but some don’t. What is different about the people who don’t?”

– David J. Tenenbaum

How did galaxies form? It’s a cardinal mystery of the early universe. Microwave radiation created 380,000 years after the Big Bang shows a smooth array of molecules, spread out like a fog. The contrast to the situation one billion years later is complete: by then, matter was concentrated in stars and galaxies, separated by empty space.

Nowadays, most galaxies hide at least one super-dense black hole, whose gravitation prevents even light from escaping. Until now, nobody knew about black holes in the earliest galaxies.

Yesterday, Ezequiel Treister of the University of Hawaii and colleagues reported that most or all of the earliest galaxies also had black holes.

A problem of roots

The data illuminates the ultimate roots question – how our universe formed its present structure, and in particular, what happened during the billion years after the Big Bang banged about 13.7 billion years ago.

For 380,000 years, “During the embryonic universe, the fluctuations in density were about one-one thousandths of a percent, but over a billion years, structures developed,” Alexey Vikhlinin, author of a commentary in Nature, told The Why Files. “These galaxies are essentially the same type of objects in the present universe,” says Vikhlinin, an expert in X-ray astronomy at the Harvard-Smithsonian Center for Astrophysics.

How did we go from the primordial fog to a universe with ultra-dense galaxies, neutron stars and black holes separated by a vast nothingness where each cubic centimeter has about one lonely atom?

The vast epoch of ignorance, Vikhlinin says, “is called the dark age because little has been observed, and one of the major questions in astrophysics is how this transformation took place.” The new observations show that roughly the same proportion of matter (excluding the enigmatic dark matter and dark energy) was concentrated in galaxies and black holes then as now.

“These results show that pretty much every galaxy must have contained a substantial black hole, similar to today,” says Vikhlinin, “but this is the first observation that the relationship between galaxies and black holes that exists today, existed 1 billion years after the Big Bang.”

An extraordinary step

In the study, Treister and colleagues correlated long exposures from

Hubble Space Telescope, which can see extraordinarily distant (and ancient) galaxies, and

Chandra X-ray observatory, which picked up X-rays from distant, unidentifiable sources.

By pinpointing the source of Chandra’s X-rays on Hubble’s galactic snapshots, the scientists located ancient black holes inside some of the first galaxies.

The study benefited from three features, says Vikhlinin. “The necessary Chandra and Hubble data were taken only recently, and the observations were immediately made available to every interested scientist,” along with some money for their interpretation.

Treister also looked at the highest energy range that Chandra can detect, Vikhlinin adds. Because Chandra’s mirrors are more sensitive to lower-energy X-rays, “most people work in this region.”

The newly detected black holes produced a surprising result – that the basic structure of the universe has not changed terribly much in the 12.7 billion years since that ancient light embarked toward a planet that did not yet exist.

The “so-what?” part

Although the study shines some light on the presence of black holes and galaxies during the dark age, it does not provide a complete answer, says Vikhlinin. “It definitely seems as if galaxies and black holes have evolved in parallel. The growth of one controls the growth of the other, and vice versa, but the nature of the process and why they evolve in parallel is not entirely clear.”

Logically, a black hole would require a galaxy to provide the cold gas that it inhales. (This gas heats up as it enters the hole, creating the black hole’s X-ray signature; it also supplies material for the stars in the galaxy.)

But why a galaxy would need a black hole is less clear, Vikhlinin says. “We don’t know if galaxies can form in regions that initially don’t have the right conditions for the growth of a black hole. Maybe whenever a galaxy starts to grow actively, it makes a black hole in the center.”

Although the new evidence for an unchanging relationship between galaxies and black holes narrows the possible explanations, the formation of the first galaxies and black holes “remains one of the biggest unsolved problems in astrophysics,” Vikhlinin says.

– David J. Tenenbaum

Japan, a world leader in earthquake engineering, has been paralyzed by a series of giant waves that followed one of the most violent earthquakes in a century.

Although the magnitude 9.0 quake on Mar. 11, 2011, apparently did not collapse high-rise buildings, the ensuing tsunamis flattened vast areas along the northeast coast. The death toll is swelling steadily as bodies wash in on the surf, and citizens and Japan’s Self Defense Forces scour a landscape turned upside down by inconceivably powerful waves.

The news recalls the estimated 250,000 people who perished, mainly on the Indonesian island of Sumatra, in the 2004 “Christmas tsunami” that followed a huge, offshore quake. (Both Japan and Indonesia are volcanic lands in the Ring of Fire, which partly surrounds the Pacific Ocean in a giant series of subduction zones and volcanoes.)

Shortly after Japan stopped shaking at 2:46 pm local time on Friday, March 11, we began hearing about troubles at a series of nuclear plants. After the reactors automatically shut down during the quake, emergency systems for removing heat still being generated in the reactors were routinely switched on.

But because the electric grid was down and the standby generators were damaged — perhaps by seawater — the emergency cooling failed. By Tuesday, March 15, three reactors had exploded, a fourth was burning, radioactive material was airborne, reactor workers were being evacuated, electricity was growing short in Tokyo, and the crucial containment vessels were under severe threat if not already breached.

With the first nuclear meltdowns since Chernobyl, in 1986, under way, global stock markets were crashing.

What causes tsunamis?

As Japan licks its wounds, The Why Files wants to know what causes tsunamis. How do they travel across the ocean? How they have impacted coastal people through history? Can we reduce our vulnerability to nature at its most cataclysmic?

Graphic: Anthony Liekens

Movement of the sea floor translates into waves at the surface.

Tsunamis — once slangily called tidal waves — are extremely powerful waves caused by large undersea disturbances. (“Tsunami” derives from Japanese for “harbor wave,” reflecting the fact that harbors can concentrate their energy. True tidal waves are the slow oscillations that drive ocean tides in response to solar and lunar gravity.)

Although landslides and volcanoes cause some tsunamis, probably 95 percent result from underwater earthquakes that contain a strong vertical motion. Such quakes often occur where one of Earth’s tectonic plates dives, or “subducts,” beneath another.

Like the Sunda trench near Sumatra, the subduction zone in the Japan trench is notorious for large earthquakes, says Timothy Masterlark, an associate professor of geological science at the University of Alabama. Although the timing is always uncertain, he says, “The history was known, big earthquakes were known, and even though the people and government went to great lengths to prepare, at some level … there is simply nothing they can do.”

Lessons from Sumatra

Masterlark, who has studied the giant, 2004 earthquake and tsunami in Sumatra, says the magnitude 9.0 earthquake in Japan likely broke a fault stretching at a shallow angle from the sea floor roughly 150 kilometers beneath Japan, along a trench several hundred kilometers in length.

We asked Masterlark how, if the slip was mainly horizontal, the rocks had enough vertical movement to cause a tsunami. “In Sumatra, we found a shallow slip created some vertical movement because the rock at the surface was softer, so the fault became more vertical, which changed the slip from mostly horizontal to mostly vertical.”

To imagine how vertical movement of the seafloor causes a tsunami, imagine making waves by throwing a stone in a pond. Even though earthquakes disturb the bottom of the water, the analogy works: just as a larger stone, thrown faster, makes a larger wave, the size of the tsunami depends on extent and speed of the ocean-floor movement.

The tsunami is usually most intense close to the earthquake: as waves spread from the epicenter in a typical arc-shaped pattern, their energy also spreads out.

Spread out, but still powerful

One factor that distinguishes tsunamis from more familiar waves is their extreme wavelength. On the open ocean, the peaks of waves may be 300 kilometers apart, and they may travel at 500 to 600 miles per hour. Even though they can keep pace with a jetliner, you wouldn’t see a tsunami from the cockpit of a jet. A killer tsunami may be only 2 feet tall in mid-ocean — far too small to be noticed from an airplane or even a ship, yet it can carry huge amounts of energy across the Pacific.

All that kinetic energy can hide in waves we can barely see because long-wavelength waves are extremely deep, and the massive amount of water moving beneath the surface contains enormous energy.

In deep water, boats can ride the worst tsunamis without noticing them; but when they reach shallow water and “run aground,” these waves become dangerous.

Like all waves, tsunamis slow when the lower part of the wave encounters the upward-sloping ocean floor. But while the front of the wave slows, the wave behind is still moving faster, causing a giant pile-up at the front, and the kinetic energy that was spread through the ocean depth concentrates in a towering wave at the surface.

Wild waves

It is these surface waves — which can be 10 meters high or taller as they cross the beach — that cause the utter destruction of tsunamis. Like all waves, tsunamis have both a rising and a falling motion, says Masterlark. “Depending on where you are with respect to the earthquake, you may first see a wall of water, or the opposite, the sea retreating.” In 2005, during a research cruise to Sumatra, “We were told that the tourists had heard that the ocean was retreating, and saw this as a great holiday, ‘Let’s walk on the seashore,” and this wall of water came in and killed them. This was a great warning, when they saw the water retreat, they should have headed away from the shore.”

Tsunamis have other quirks. They can be spaced as much as one hour apart, so subsequent waves can kill those who return to help victims of earlier waves.

In 1998, Harry Yeh, a civil engineering professor now at the University of Oregon, told us that tsunamis can have decidedly unconventional behavior. In one case, he said, a tsunami destroyed houses in a cove without damaging a house on an unprotected headland: “It’s the exact opposite of what a storm wave would do.”

A warning

Modified from original image by NASA

Location of foreshocks, aftershocks and the March 11 Japan earthquake (M 9.0). Circle size represents quake magnitude. Dotted lines = foreshocks; solid lines = aftershocks

The Pacific Tsunami Warning Center, established in Hawaii in the wake of the deadly 1946 tsunami, is a nexus in the global warning network. Since almost all tsunamis originate in earthquakes, the warning centers rely on data from seismographs, many of them located on the unstable ring of fire.

Tsunami warnings are now triggered automatically, says Masterlark, based on measurements of earth movement. “Seismographs are excellent because in seconds they can tell that a quake of some magnitude, big enough to trigger a tsunami, has occurred. This information can automatically trigger a warning in seconds.”

In tsunamis, seconds saved can translate into lives saved.

Researchers are working to use global positioning system (GPS) data to refine size estimates, Masterlark adds, to give “a more refined view of the potential risk, but this takes a little longer and is still in a research mode.”

Further confirmation of the size of the wave may come from special purpose ocean buoys, if they are in the right place, Masterlark says. “But they only work once the tsunami has already arrived, so they can only confirm or help refine the warning.”

Tricks of the tsunami trade

In terms of generating tsunamis, not all underwater earthquakes are created equal, says Andrew Newman, assistant professor of earth and atmospheric sciences at Georgia Tech. “A few times a decade, we have what we call ‘tsunami earthquakes’ that create a tsunami that’s much larger than would be expected for the magnitude of the earthquake,” largely due to a shallow rupture. “Usually a magnitude 7.8 earthquake would create a tsunami that might rise only 20 centimeters to 1 meter [when it reaches land], but one in Sumatra last year created a 17-meter tsunami.”

These large tsunamis come from a smaller break in the ocean floor, and so contain relatively little energy and do not travel well across the ocean, Newman says. But they also offer less warning because local people do not feel the massive shaking associated with a major tsunami.

Newman and colleagues have developed software to detect the peculiar signature of the tsunami earthquake, and are now running it on a research basis. “We get an earthquake or tsunami warning within four or five minutes, our algorithm starts processing, and a few minutes after that, the system sends email to the Pacific Tsunami Warning Center and the U.S.G.S. [Geological Survey],” Newman says.

Although the Japanese had little time between the earthquake and the tsunami, Newman says the national warning system did work. “In some ways, you have to look at real success in Japan. They have developed a substantial tsunami warning system, and it worked in as quickly as three minutes. People did evacuate, for the large part. Much of the video you see is from helicopters, or people watching from two or three stories up in buildings. There is only so much you can do with these events; this is a massive force.”

But the rising casualty counts highlights the deadly role of proximity to the quake, says Masterlark. “The very sad part is that because the quake was so close to the coast, they had very little warning; the time between the earthquake and the tsunami was minutes.”

More distant regions had adequate warning, Masterlark adds. “We had several hours before the wave reached Hawaii, and so were prepared. But Japan, unfortunately, even if you knew it was coming, you had only minutes, and that’s not enough time for many people to get to higher ground.”

Photo: Sarah Ruth

Basic tsunami safety

Public education and quick personal action remain the only ways to reduce the tsunami death toll:

1. Be on guard for strong earthquakes, which can spark a tsunami. If you feel one near the water, run inland.

2. Heed the warnings, and stay tuned to emergency radio stations.

3. Never go down to the beach to watch for tsunamis — they move much faster than you can run. People die doing this.

4. Most structures in the danger zone provide no protection. However, the upper stories of tall, reinforced concrete hotels can provide refuge if you have no time to move inland or to higher ground.

5. A tsunami is a series of waves. Don’t go near the water until you hear the all-clear from emergency authorities.

Following fatal footsteps?

Seismologists are loathe to predict earthquakes, but in the past decade or two, they have recognized that earthquakes occur in series along major faults in Turkey and Sumatra, as big quakes place extra stress on the adjacent fault. In Sumatra, a violent series of quakes began in 2004 with a magnitude 9.1, a magnitude 8.7 in 2005, a magnitude 7.6 in 2009, and a magnitude 7.7 in 2010.

The large quake in 2005 did not cause a major tsunami, but its timing, just three months after the Dec. 26 monster, suggests a compelling reason to focus intensively on the earthquake zone in the Japan trench, says Masterlark. “I am not trying to be alarmist, but I’m trying to look at where earthquakes have occurred along nearby faults to identify faults at risk. We’ll bring in numerical modeling and try to predict this as fast as possible. Time is of the essence, as we saw in Sumatra.”

As deadly American drones work the skies over Afghanistan and Pakistan, we got to wondering how similar remote-control approaches are contributing to science. In science, as in war, leaving the staff behind can slash costs and allow sustained exploration of no-go zones.

Part of the story is propulsion: New science vehicles can travel long distances through the ocean and atmosphere with minimum energy. Brains-on-board also matter: Computers enable these super-sensors to make decisions and work long stretches with little or no back-seat driving.

The result is a lot of science per gallon.

Although the vehicles we’ll look at have scientific purposes, they get major financial and technical support from the Department of Defense, proving that military and peaceful pursuits are inextricably linked in extreme environments.

If you dig the deep ocean, WHOI — the Woods Hole Oceanographic Institution on Cape Cod — is a good place to be. The renowned saltwater scientific outfit has a new, deep-water explorer that works without a lifeline.

Meet Sentry, which can take photos and make chemical and geophysical measurements down to 4,500 meters depth, and has worked two high-profile environmental issues: global warming through methane release, and BP’s Deepwater disaster.

Sentry has been used to look for “cold seeps,” regions of the seafloor that release large amounts of methane, says Chris German, WHOI’s chief scientist for deep submergence. “Cold seeps are like the overlooked younger sisters of hydrothermal vents,” the “black smokers” that release superheated fluids and anchor unique ecosystems at the sea floor, usually in mid-ocean.

Cold seeps are located closer to the continents, and “are not as spectacular thermally or geologically, but they do have some of the same chemistry,” says German, “and a lot of the same kinds of animals, even the exact same species.” Cold seeps may explain the distribution of deep-sea organisms around the ocean, he adds. “We want to understand … whether animals are using these locations as stepping stones.”

Most cold seeps were found by accident, but German thought Sentry could detect subtle chemical clues, and last October, he got to test that idea at an underwater landslide off the coast of Norway. The landslide had released pressure on a material called methane hydrate, and a large amount of methane was bubbling from the seafloor mud, creating a “mud volcano.”

Methane is a much more powerful greenhouse gas than carbon dioxide, and given the staggering amount of methane held in methane hydrates, such releases could create a nightmare feedback: warming releases methane, which traps more heat, causing more warming that releases more methane.

Getting engulfed

By prowling around the known cold seep near Norway, German confirmed the detection hypothesis.

Then, the day after Sentry returned to Woods Hole, a real-world opportunity appeared for the new technique.

Biologist Charles Fisher at Penn State was about to embark on a mission into the aftermath of BP’s blowout in the Gulf of Mexico, and he wanted help locating a coral patch to compare to another he’d already located 1,200 meters deep, 11 kilometers southwest of the blowout.

That coral was coated with a brown goop that looked suspiciously like crude oil. Could Sentry locate, for long-term comparison purposes, a similar coral outside the oil plume?

Fisher was part of a National Science Foundation-sponsored “rapid response” cruise to the Gulf, but German was still unpacking. “We’d have two weeks to turn around and get going, and I went to our guys Monday morning and asked, ‘Can you do this?’”

The maintenance crew figured out who would miss what weekend, and they agreed to do it, German says.

Cold seeps and deepwater coral in the Gulf of Mexico are linked, German explains, because the coral live on bare rock, which is often carbonate, and carbonate rock forms at cold seeps when methane is oxidized into carbon dioxide. “So beneath every healthy deep coral, is an active or historic cold seep.”

Suddenly, a theoretically interesting search technique became relevant to the biggest American oil spill in a century.

“Flying” with a map

Based on oil-industry data about the sea bottom, Sentry visited one location southeast of the Macondo well and found no coral. But at the second location, German says, “We hit pay dirt. We flew backward and forward, and found an active cold seep and evidence for tube worms, mussels and coral.”

Ocean-floor research seldom moves so fast, German says, and within hours, he was one of three people to visit the spot in Alvin. “In 36 hours, we went from nothing other than a hunch, to having a topographic map and photos,” German says. “We dove to the sea floor, and there was no mysterious driving around in the dark. Within 15 minutes, we drove to the site because we had a perfect map of where to go.”

In fact, German was holding a fresh, glossy photo of the target, taken less than two days previously.

Sub-terra cognita? Not!

And so is the ocean bottom, as people often say, still less familiar than the far side of the moon? German insists that it still is, despite years of research and an increasingly capable flotilla of deep-sea ships. “In December, in the Gulf, I could see at least 10 to 20 oil rigs… but I’m pretty sure, driving across that seafloor a couple of hours offshore from the United States, that nobody ever laid eyes on it before.”

A recent survey of marine biodiversity shows a chain of ignorance stretching across the Pacific, located near regions of extremely high biodiversity near the Philippines and Australia, German says. “In many of those locations, they’re 300 miles square, there have been fewer than 50 biological measurements in the history of the ocean. This is a chain across the South Pacific ocean, the single biggest contiguous ecosystem on the planet, and it has not been studied.”

And that’s the rule, not the exception, German says. “Close to one-half of the planet is at least 3,000 meters deep, and it’s much further away [and deeper] than the Gulf. From satellite altimetry we have an idea where the bumps are on the seabed, but we don’t know what’s going on; we have a vanishingly small idea.”

Deep water may be the sexiest place in oceanography, but long-term studies are also difficult and expensive in shallow waters, especially if they are remote, icy, stormy, or all three. Propellers, the standard way of moving through water, require a lot of energy and quickly drain batteries on artificial fish.

Gliding — think of soaring like a hawk as opposed to flapping like a sparrow — is a much more conservative approach.

And gliding is the MO of Seaglider, a project built by the University of Washington with money from the Office of Naval Research and the National Science Foundation. Using battery power, the glider alters its buoyancy, causing it to rise or fall through the water. By altering its center of gravity and adjusting its fins, the metal fish moves horizontally with minimal amounts of electric current.

How minimal? In 2009, a Seaglider traveled a record 3,050 miles through the North Pacific during a 9-month journey, without the caress of a human hand or an electric transfusion.

Costing “only” about $100,000 apiece, about 60 gliders are working around the globe, says Craig Lee, a principal oceanographer at UW’s Applied Physics Laboratory, recording basics like temperature, salinity, dissolved oxygen and optical characteristics of its surroundings.

In 2008, south of Iceland, gliders and floats studied carbon uptake by phytoplankton — floating plants that bloom in spring and play a major role in the global carbon cycle. The goal was to follow “parcels” of water during the entire bloom — which ends after some weeks when plankton are eaten or sink in the water. Both processes can remove carbon dioxide from the atmosphere for long-term storage, and therefore have implications for global warming.

“We were trying to learn what drives the carbon flow,” says Lee. “Nobody had done this before: the Seagliders and the buoys had the persistence, the ability to be there for the entire duration of the bloom. You would have to schedule a ship one year ahead, and … if you got there on time, it would be too expensive to keep the ship out there for the whole bloom.”

If ice is nice, under ice is nicer!

In 2009, a Seaglider spent 51 days in Davis Strait, the frigid water separating Greenland and Baffin Island, traveling more than 450 miles under the ice. The Strait is a chief source of melt-water from the frozen Arctic Ocean.

Climatologists worry that a rush of cold, fresh water through the Strait could alter the warm Gulf Stream and freeze Northern Europe.

Getting measurements from Davis Strait is expensive and dangerous, especially considering how much of it is under ice. But the Seaglider did just fine, says Lee. “This was very exciting, that ability to stay out there for a long time, and the ability to get to places that otherwise would be difficult. In winter in the North Atlantic, nobody wants to be there…”

The fish navigated under the ice using five anchored sonar beacons that created an undersea version of GPS, Lee says. Ten times, using its software, the glider found holes in the ice, poked its nose through them, and phoned home via satellite telephone. “It tries to sense ice by looking at the temperature of the water,” says Lee. “It emits a ping and tries determine whether ice is overhead, and it has a climate map that tells it, for a given position at a given time, is ice likely to be overhead? Using all that information, it decides whether to surface.”

During those famous North Atlantic storms, “It just keeps working, it does just fine, continues to navigate, continues to report. We’ve been in 40-foot seas, with 60- to 80-knot winds, and everybody’s happy, although it takes a little longer to get a phone call through.”

The glider carries a quarter for the phone call, but no Dramamine…

A fruit of the military’s desire to see everything from a safe vantage, Global Hawk is a secretive, high-flying, pilot-free jet that can fly at 60,000 feet for 30 hours, non-stop.

For its occasional forays into peaceful work, Global Hawk carries a large cargo of scientific instruments that can monitor light, pollution, ozone, water vapor, weather, clouds, incoming and outgoing radiation, even particles smaller than 1 millionth of a meter across.

The Hawk, which flew scientific missions from NASA’s Dryden Flight Research Center in California in April, 2010, can also be used for earth observation, such as tracking algal blooms in the ocean, vegetation on land, and various resource issues.

Hawk has tracked pollution from Asia above the North Pacific as it moves toward North America and looked at large-scale atmospheric circulation, which influences weather and the distribution of radiation-blocking high-altitude ozone.

We could not get through to a source at the National Oceanic and Atmospheric Administration, which plays a role in Hawk’s science, but we grabbed a press release issued after Hawk’s first environmental flight.

According to Paul Newman, an atmospheric scientist from NASA, “The Global Hawk is a revolutionary aircraft for science because of its enormous range and endurance. No other science platform provides this much range and time to sample rapidly evolving atmospheric phenomena. This mission is our first opportunity to demonstrate the unique capabilities of this plane, while gathering atmospheric data in a region that is poorly sampled.”

In their quest for data on the deep, scientists have gotten a trickle of info from sensors attached to deep-diving marine mammals. In November, 2009, the Scripps Institution of Oceanography launched SOLO TREC (Sounding Oceanographic Lagrangrian Observer Thermal RECharging vehicles; glad you asked?), a bobber that can sink 500 meters into the ocean, then return to the surface to report via satellite to scientists who may prefer sipping lattes at a Java Joint to crowding the rail on a topsy-turvy research ship.

Let’s call this Solo, and let’s agree that it’s a strange vessel. Solo can adjust its buoyancy, but lacks propellers and cannot drive laterally, so its location is at the mercy of the currents.

Solo records basic ocean conditions, but the real accomplishment is proving that its power system needs no recharging and could, theoretically, operate more or less forever – or at least until it breaks or barnacles or plants foul the fish up and slow it down.

Solo had already completed 300 dives by March, 2010, and although it sounds like a perpetual motion machine, it actually sucks its energy from the ocean as it rises toward the surface:

According to Yi Chao of the Jet Propulsion Lab, a Solo principal investigator, “This technology to harvest energy from the ocean will have huge implications for how we can measure and monitor the ocean and its influence on climate.”

Funded by NASA and the U.S. Navy, Solo’s technology is also obviously useful for monitoring animals and the movement of ships and submarines.

Skeptical about global warming? 2010 has just tied 2005, making these the two hottest years on record. And nine of the 10 warmest years on record have occurred since 2001.

Photo: williumbillium

Was New York’s epic blizzard last month related to climate change?

But temperature is only part of the story. After a year that saw epic floods in Pakistan and California, massive floods have swamped Brisbane, Australia, population 2 million. Russia was toasted by a record heat wave last summer. Europe and, of course, New York were smothered by giant snowstorms.

And we just read that 2010 had the heaviest precipitation on records that date to 1880.

So we have to ask: Is this normal weather, or is this climate change in action?

And as greenhouse gases continue to accumulate in the atmosphere, what will happen the day after tomorrow?

There is good theoretical reason to think that an accelerating greenhouse effect will affect weather: Add greenhouse gases like carbon dioxide and methane to the atmosphere, and they trap more heat. In hotter conditions, more water evaporates from the ocean, which eventually falls as precipitation. Heat is energy, and more energy in the ocean and atmosphere provides more power to drive intense storms.

These questions are devilishly difficult to answer. It’s a big planet, and assessing conditions during the past few decades, and making projections for the future, is a gnarly task. Climate models are better at getting the big picture than making regional forecasts for future weather. Data records are incomplete, especially as we delve further in the past.

Graph: Progress Report of the Interagency Climate Change Adaptation Task Force: Recommended Actions in Support of a National Climate Change Adaptation Strategy, October 5, 2010

If you doubt that warming temperatures have anything to do with carbon dioxide, the primary greenhouse gas, here’s something to think about. Horizontal divider shows average temperatures, 1901-2000.

Nevertheless, let’s ask our question about both recent weather data and future forecasts.

Record temperatures

As the climate warms, one easy prediction is that record warm days will become more common, and record colds will be less common. When Gerald Meehl, a senior scientist at the National Center for Atmospheric Research, compared the number of record daily highs to the number of record daily lows in the U.S., he found they were roughly equal in the 1950s.
Today, he says, “for every two record highs, there is only one record low. If there was no warming going on, the ratio would be one to one, so we are shifting the odds toward having a better chance for setting a record high versus a record low.”

Meehl says Australian data show the same thing.

Even though the climate has warmed by only about 0.6° C, he says, “This shows that even with a very small change in average temperature, about 1° Fahrenheit, we can get a pretty noticeable change in the extremes.”

Click here to view the embedded video.

At some point, we may look fondly upon today’s two-to-one ratio, as climate models suggest the ratio will reach 20 to 1 by year 2050 and 50 to 1 in 2100. Yet even then, when the U.S. average temperature may have risen by several degrees C, “We still get some daily record low temperatures,” Meehl says. “We still get extremely cold weather, although it will happen much less frequently.”

Today, he notes, “When there’s a cold snap, people ask, ‘What happened to global warming?’ But even with warming, it will still get cold, but not extremely cold, and not as often.”

Precipitous rise in precipitation?

Rain and snow are two ways that the atmosphere feeds life on the planet. A hotter atmosphere has the ability to hold more moisture because more water evaporates from the ocean, and warmer air can also store more moisture.

Already, says Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research, the water-vapor contained in an imaginary cylinder stretching from Earth to space has been rising 1.3 percent per decade since the 1970s.

And so warming means more potential for precipitation.

“When we review change in the hydrological cycle,” Trenberth says, “not just tropical cyclones [hurricanes and typhoons] but extra-tropical cyclones and individual thunderstorms, the evidence from around the world is that when it rains, it rains harder, when it snows, it snows harder. This is consistent with the understanding we have, the theory.”

That is also happening in the United States, where days with intense rain and snow have been increasing, says Meehl. “When it rains, it pours, we see this in observations, and models show an increase in the future.” For example, a summary published in 2007¹ found that, “Over the last century there was a 50% increase in the frequency of days with precipitation over 101.6 mm (four inches) in the upper Midwestern U.S.”

However, land use plays a role in some observed precipitation changes, says James O’Brien, emeritus professor of meteorology and oceanography at Florida State University. “We studied heavy rainfall over 62 years in Orlando, Fla., and did a simple thing: We divided the time into two periods of 32 years each, and looked at the probability of one or more two-inch rainfalls.”

In the recent period, during almost all non-summer months, Orlando had a big increase in heavy rain, but Gainesville, 40 miles away, did not. “The cause in Orlando is absolutely clear,” says O’Brien. “It’s Disney World. It’s all the roads, the concrete, which act as a heat sink. In winter, a cold fronts hits a bubble of heat caused by this heat island, and it kicks up a storm and you get more rain.”

Heavy rain = heavy drought?

Even if total precipitation does not change, there are consequences to the newer “when-it-rains-it-pours” precip pattern. Heavy rain runs off rather than percolating into the soil, so instead of feeding plants, it can cause soil erosion and floods. If, as some models suggest, extreme precipitation increases in springtime, when the ground is still frozen, “that has a significantly different impact than extreme rainfall during summer,” says Daniel Vimont, an assistant professor at the Center for Climatic Research at the University of Wisconsin-Madison, because the rain cannot enter the soil and must run off.

Heavy rain can also contribute to drought by drying the atmosphere, Meehl says. “We have to take into account the number of days between precipitation events. On a map of North America, almost everywhere intensity shows an increase to date, and a projected increase, but we also see dry days increasing, like in the southern tier of states and especially the Southwest. When it rains, it rains really hard, but there are more days between rainfalls. On average, you are getting less total precipitation, but the risk for floods has increased because of this intensity increase. Over long periods, we are seeing drier conditions, because the number of days between events is also increased.”

Facing a wave of drought

A trend toward drought is already under way, according to a 2004 study by Aiguo Dai of the National Center for Atmospheric Research, which found that the percentage of Earth’s land area stricken by serious drought had more than doubled between the 1970s and the early 2000s.

The future seems no more benign. Last October, Dai published a review, based on 22 computer climate models, that projected a major expansion of drought over the next 30 years. The affected area includes the breadbasket regions of North and South America, most of Africa and Australia, and parts of China and neighboring countries.

According to the study, the western two-thirds of the United States will be significantly drier in the 2030s, after which matters will only get worse.

In general, the only places that will see more precipitation are in the extreme north — Northern Russia, Scandinavia, Canada and Alaska.

So reindeer need raincoats…

But seriously, “We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community,” Dai says. “If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous.”

Cyclones, typhoons and hurricanes

In terms of extreme weather, nothing beats the tropical storms variously called typhoons, tropical cyclones or hurricanes — for their winds, high seas and astonishing rainfalls. So hurricanes are the natural focus of study on the past and future effects of global warming.

In 2005, Hurricane Katrina played the starring role in a series of powerful hurricanes that pounded the Gulf of Mexico and Caribbean, and we reported that hurricanes were packing more power in a warmed planet.

Then came a counter-rebellion: scientists began questioning whether hurricanes were really more powerful, and noted that they were not getting more common (although everybody agrees that increasing population and development along the coasts both contribute to greater storm damage).

The chief hindrances to finding real trends in the tropical cyclones are their long-term, natural variation in strength and frequency, and the wobbly nature of data on older cyclones. In the North Atlantic, home of the best hurricane data, the quality of the data jumped when airplanes began flying into hurricanes in 1944, and again when satellite tracking began around 1970. Data on older Pacific and Indian Ocean storms are even more questionable.

To explore how global warming will affect tropical cyclones, the World Meteorological Organization set up a team under the leadership of Thomas Knutson, of the Geophysical Fluid Dynamics Laboratory. Knutson’s group projected that hurricanes, globally, will become 6 percent to 34 percent less common by 2100, despite the warming trends².

The counterintuitive reduction may be due to wind. These storms need a warm ocean to provide energy, “but you also need an atmosphere that cooperates,” explains Charles Conrad, an associate professor of geography at the University of North Carolina and director of the Southeast Regional Climate Center. Wind shear, a change in wind velocity with altitude, can blow a developing storm apart. “Some global climate models suggest that more wind shear over the tropical and sub-tropical Atlantic may inhibit cyclones, so when you put that together with higher sea-surface temperatures, this suggests that when a system can develop, it will be stronger.”

A question of intensity

Given the rickety data on older storms, Knutson’s group concluded that “it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes.” According to team member Christopher Landsea, science and operations officer at the National Hurricane Center, “Every single paper in the peer reviewed literature, looking at the theoretical side of hurricanes and global warming, or the climate model simulations, says the same thing. The changes today are very, very tiny, maybe 1 percent stronger, due to manmade global warming.”

But another member of the team begs to disagree. “I think the evidence is fairly unequivocal that there has been an increase in intensity,” says Kerry Emanuel, professor of tropical meteorology and climate at Massachusetts Institute of Technology. To gauge intensity, Emanuel used wind speed, measured at six-hour intervals, to calculate a “power dissipation index,” fancy lingo for the amount of energy that enters the hurricane.

Graph: Weather and Climate Extremes in a Changing Climate³

Heat energy from the ocean powers hurricanes, and storm intensity closely follows changes in sea surface temperature in the North Atlantic. “Power dissipation” is a measure of the storm’s total power, based on a cube of maximum wind speed.

The index, he says, shows that recent hurricane intensity is “beautifully correlated with ocean temperature in the tropics,” and those warm seas, in turn, result from accelerating greenhouse warming. Changing levels of greenhouse gases and reflective aerosols in the atmosphere “are the cleanest explanation for what happened with hurricanes,” Emanuel says. “I think there is a strong [human-caused] signal in Atlantic hurricanes over the last 40 years.”

Tower of power

And what of the future? The Knutson team projected that average maximum winds would increase 2 percent to 11 percent by 2100, so “a substantial increase in the frequency of the most intense storms is more likely than not globally, although this may not occur in all tropical regions.”

Although the group wrote that intense tropical cyclones, “deserve particular attention, as these storms historically have accounted for an estimated 85 percent of U.S. hurricane damage,” Landsea said, “That’s a very small increase, a long ways in the future,” and it could be offset by a decreasing frequency of storms.

In the world of climate, it’s usually possible to find another voice, and last year, a modeling study⁴ projected that the number of category 4 and 5 storms will almost double by 2100. (Category 5 includes the strongest hurricanes.)

We asked James Kossin, a scientist with the National Oceanic and Atmospheric Administration, who has studied hurricanes since 1987, about those results, and he told us, “There is a lot of uncertainty in our understanding of how tropical cyclones respond to their environment and to changes in their environment.”

Linking changes in hurricanes to human-caused climate changes is “very challenging,” said Kossin. “I have medium confidence that climate change could lead to the strongest storms getting stronger” globally.

Emanuel, however, says the creators of these models “freely admit they will not model intense hurricanes, they don’t have the resolution. What does a 2 percent to 11 percent increase mean if the models are constitutionally incapable of having hurricanes? And this is what the models are telling us, but what does nature say? It tells us that hurricanes intensity is changing much more rapidly.”

Emanuel reminds us that storm destruction equates to at least the cube of wind speed, and therefore, a small increase in maximum wind can mask a much larger increase in intensity and damage.

From here, gentle reader, the arguments devolve from murky to truly obscure. We promise to report back in a few years, but we’re happy to note that this dispute, however contentious, is being fought in print by civil scientists who can cooperatively ponder on our climatic future.

Easy questions can be tough to answer

We’d love to know if warming is affecting wind, but the records do not support such a comparison, says Dan Vimont. In a study on climate change in Wisconsin, for example, “We started to look at wind, but there is not as much observational data. There are 200-odd temperature-precipitation gauges around Wisconsin reporting daily, but … it’s difficult to find a continuous record from a gauge that is monitored well.”

The reality is that as much as we’d like to attribute particular events like the floods in Pakistan and Australia to climate change, we may never know. “For any given event, it’s really hard to gauge how much climate change has contributed,” says Claudia Tebaldi, a climate statistician with the non-profit Climate Central. “Even for heat waves, where it’s obvious that as climate warms you would expect more intense heat waves, [you have to acknowledge that] a given heat wave may have happened anyway without climate change.”

Why do some rocks break so easily once an earthquake begins? In a giant quake, the fracture, where the two sides of the fault grind against each other, can extend dozens or hundreds of miles. The question has met several answers over the years.

According to one theory, rocks get hot enough at the break to form a slippery layer of glassy rock along the fault. But that is not entirely satisfactory, says Ze’ev Reches, a professor of geoscience at the University of Oklahoma, because large earthquakes can form where the rocks are too cool to form glass.

“For some reason, friction seems to decline during a break, but what is the mechanism?” he asks.

In a laboratory study in this week’s Nature, Reches and David Lockner of the U.S. Geological Survey showed that a thin layer of rock powder that forms at the break causes a rapid drop in friction, which allows the break to spread further and faster down the fault. “The powder itself is a lubricant and it reduces the friction when it forms,” he says.

• Haiti. January 12, 2010. Magnitude: 7.0.

  Photo: United Nations Development Programme
  

• San Francisco, CA. April 18, 1906. Magnitude: 7.8

  Photo: Chadwick, H. D./NARA National Archives and Records Administration
  

• Chile. February 27, 2010. Magnitude: 8.8, and March 5, 2010. Magnitude: 6.6.

  Photo: Nico Ibieta
  

• Indonesia. September 30, 2009. Magnitude: 7.5.

  Photo: United Nations Development Programme
  

• Turkey. August 17, 1999. Magnitude: 7.6.

  Photo: yolalmis
  

Rock ‘n rotate

To test rock samples, the researchers used a press that rotated one sample against another, producing a motion that was more representative of actual earthquakes, and also much longer and faster than previous researchers have studied. The study showed that a thin layer of rock powder can weaken the fault by at least 50 percent, Reches says.

The results concern how rock can slip once a fault breaks. It would be nice to know how the first rupture occurs, Reches says, but conditions in fault zones are so varied “that there is always a place where it’s significantly weaker, or is under a significantly higher load, so it starts moving. The question becomes, how far will this movement go?”

And the answer depends on how much friction remains in the broken portion, he says.

The rotary rock-grinder also showed that the powder, called gouge, ceases to lubricate within hours or days. “Everybody has seen the powder in faults and in experiments, but it was always taken for granted that the gouge does not change its properties,” Reches says. “What we have discovered is fundamentally different: The gouge has to be formed fresh, each time, to obtain this lubrication.”

Courtesy Ze’ez Reches

A close-up of the test apparatus shows lubricating powder that formed when rocks were ground against each other to simulate earthquake movement.

Break, dancing

The original powder is composed of grains that are “a few tens of nanometers across, but then because of adhesion between the grains it starts forming much larger clusters,” Reches says. The small grains can slip against each other, “but once they form these clusters, it takes a lot of energy to break them, so friction rises.”

“The internal workings of earthquake faults is one of the great unsolved problems of geophysics,” says Harold Tobin, a fellow fan of faults who is professor of geoscience at the University of Wisconsin-Madison. “Understanding the friction and mechanisms inside a fault, as it suddenly goes from hundreds of years of building up tremendous stress to rupturing in an earthquake, would help us understand why, where and when earthquakes occur. Experiments like the ones reported by Reches and Lockner are a key tool for getting at how earthquake faults slip.”

The study, Tobin says, is “a window on how an initial cracking turns into an earthquake. In my view, the study is not a game-changer in terms of our understanding of earthquake faults, but it does provide some solid data that will feed into better theories and models.”

Bearing it out

The study could help explain why the many tiny quakes that occur each day do not set off major quakes, Reches says. “In Oklahoma, we have magnitude 2 or 3 quakes but they don’t grow, because the conditions surrounding the break are not suitable. Why an earthquake occurs is not related to the initiation, but to the weakness that allows it to propagate.”

Photo: Scott Haefner/U.S. Geological Survey

The San Andreas Fault in California is active and deadly.

The phenomenon could also explain the “creeping section” of the San Andreas Fault, near Parkfield, California. Beyond both ends of the 120-mile section, the fault produces lethal, magnitude 8 quakes, Reches says, yet quakes in between release less than 10,000 times as much energy. “Although it’s on such a major active fault, the creeping section accommodates the motion in a very different mode. It might be that the rocks in this zone are not capable, once the motion starts, of creating the gouge that would lubricate it.”

With medium- and large-size earthquakes, Reches says, “the fundamental issue is, what is the mechanism of the weakening? What we have found is that once it starts moving, the formation of gouge makes it much weaker than before the movement started.”

– David J. Tenenbaum