How to Destroy the Universe (4 page)

Just as earthquakes at transform faults arise because of friction between the plates, so plates that are subducting undergo the same “stick-slip” behavior—as a large mass of rock suddenly springs back into shape having
been deformed by the force of the moving plates. When this happens under water some of the energy of the quake is transmitted to the water, forming a tsunami, a giant wave, that rushes inland. These are known as “thrust” earthquakes. The density of water (a single cubic meter weighs a ton) makes them especially destructive. In 2004, a thrust earthquake off the coast of Indonesia measuring 9.2 on the moment magnitude scale (making it the second most powerful earthquake on record) threw up a tsunami that swept ashore killing 230,000 people. There are fears that a similar disaster could be waiting to happen off the coast of California, where the Juan de Fuca plate is subducting under the North American plate.

What can we do to protect ourselves in the face of such seemingly overwhelming might? The Inca civilization in Peru had a pretty good idea, 600 years ago. Many of their buildings, such as the complex at Machu Picchu, are still standing today despite being constructed in an area of extreme seismic activity. The Incas realized that making a building earthquake-proof isn't necessarily the same as making it stronger. The structures that survive today were built using a dry-stoning technique, where blocks of stone were stacked together with no mortar between them. The stones were so precisely cut that, so the story goes, you couldn't even
shimmy a blade of grass between them. But when an earthquake struck, the lack of any mortar gave the buildings the flexibility to move and sway with the tremor, instead of crumbling under its force.

In the cities of the modern world, construction without mortar or other forms of fixing simply isn't an option. However, architects have managed to apply the Incas' logic elsewhere—in a building's foundations. The technique is called “base isolation.” The building's superstructure (the part that's above ground) is coupled to its substructure (the foundations) using supports that are rigid under normal conditions but in the event of an earthquake become flexible, so that the vibrations in the substructure are not transmitted upward where they could undermine superstructure. One example of such technology is known as a “lead rubber bearing”—a support that sits under the building's superstructure and is made from rubber with a core made of the soft metal lead. The rubber makes the support flexible, while the lead serves as a “damper” to stop the rubber getting too springy. The bearings can even be retrofitted into the foundations of existing buildings. Effectively, the buildings are being given a set of shock absorbers.

Some modern skyscrapers incorporate giant pendulums in their upper levels. Known as tuned mass
dampers, the pendulums are designed to swing inside the building at exactly the same frequency as, but in the opposite direction to, the swaying of the building. So as the building lurches to the left, the mass of the pendulum bob swings to the right to counterbalance it.

Tuned mass dampers are especially effective at combating a phenomenon called resonance, where vibrations at a structure's “natural frequency” produce violent shaking that can lead to severe structural damage. To visualize how resonance works imagine a child playing on a swing. The swing makes one complete back-and-forth oscillation every two seconds. If the child's father, standing behind the swing, gives a push at exactly the same frequency—once every two seconds—each time the swing comes back toward him, the size of the oscillations will grow steadily bigger. Resonance is the reason why a truck with its engine idling will sometimes shake violently, but when the engine is revved to higher rpm the shaking subsides. Taipei 101, a 101-story skyscraper in Taiwan, sports the largest tuned mass damper of any in the world. The bob of the damper pendulum weighs a mammoth 660 tons. The damper not only helps mitigate the threat from earthquakes but also serves to steady the building in high winds.

Every year, one day in the third week of October, at 10:15 am, millions of Californians dive under tables, chairs and any other forms of cover they can find. Called the Great California ShakeOut, it's the world's largest earthquake drill. The annual drill is designed to help the sunshine state cope in the event of an unforeseen quake. Because that's what most quakes are: unforeseen. The science of earthquake prediction is, at best, shaky. It's rare for seismologists to predict accurately the date, time, location and magnitude of an earthquake. There is no way for them to gather data about rock movements deep underground. Normally, the best they can offer is probabilities. For example, after studying a particular fault for many years, using strain gauges to measure how the rock is stretching at the surface, they might be able to say that there's a 50 percent chance of a 6+ magnitude quake, somewhere along the fault line, during the next 20 years. So what prognosis do the seismologists offer California? A study by the United States Geological Survey in 2008 concluded that the probability of an earthquake with a magnitude of 6.7 or higher striking the Greater Bay Area surrounding San Francisco, sometime in the next 30 years, is about 63 percent—it's twice as likely to happen as not.

• Hurricane Katrina

• The Coriolis effect

• Hurricane hotspots

• The Saffir–Simpson scale

• Project Stormfury

• Cool hurricanes

Hurricanes are the most devastating of all Earth's weather phenomena. They are fierce thunderstorms sometimes over 2,000 km (1,250 miles) across. Windspeed within a hurricane can reach 280 km/h (180 mph). And they can be accompanied by waves 10 m (33 ft) high that sweep ashore when the hurricane makes landfall. The average hurricane cranks out energy at a rate equivalent to a 10 megaton nuclear detonation every 20 minutes. Can we ever hope to be master over such a force? Some scientists think so.

On August 23, 2005, an innocuous-sounding weather system known as “Tropical Depression 12” formed over
the Bahamas. As it began edging its way toward the east coast of the United States, it grew in strength, reaching “tropical storm” status early on August 24. At this point it was also given a name: Katrina. The storm continued to gather momentum, reaching hurricane proportions just hours before crossing Florida and entering the Gulf of Mexico. By August 28, it had strengthened to category 5, the most intense variety of hurricane. It made landfall in Louisiana at 6 am on August 29 with catastrophic consequences. At least 1,800 people were killed, and a further half a million were left homeless. However, Katrina is not the most devastating hurricane on record. That dubious honor goes to the Bhola cyclone that struck Pakistan and India in November 1970. The wall of water that accompanied it swept half a million people to their deaths.

Cyclones and hurricanes are essentially the same thing. The fundamental phenomenon is a cyclone—but cyclones cropping up in different parts of the world are given different names. A cyclone in the Atlantic Ocean, as was the case with Katrina, or in the eastern Pacific Ocean, is called a hurricane. One that arises in the western Pacific is known as a typhoon.

Cyclones begin when warm ocean water causes moist air to rise high into the sky, as far as 15 km (9 miles) up.
At this altitude the air cools, releasing its heat, and causing the moisture to condense into rain clouds. The cool, dry air then falls back down to sea level where the cycle repeats. The physics responsible for this process is known as convection. It happens because gases expand as they are heated up. This lowers the gas's density, causing it to rise—in just the same way that an object with a density lower than that of water will float on the surface of the sea. Convection is also the reason why hot-air balloons are able to fly.

If only convection were involved, hurricanes wouldn't be much to write home about. But there's another process going on that stirs things up—quite literally. It's called the Coriolis effect, named after the 19th-century French scientist Gustav Coriolis, who first wrote down the mathematics describing it. It makes the air in Earth's northern hemisphere swirl in an anti-clockwise direction (as viewed from above), while air in the south swirls clockwise.

The Coriolis effect is caused by the planet's rotation. Imagine taking a series of horizontal slices through Earth from the North Pole down to the equator. As the planet turns all the slices rotate in lockstep, each slice completing one whole revolution per day. But the diameter of each slice gets bigger as you head south, so the actual straight-line speed of the slice's outer edge increases. For example, while Earth's surface at the
latitude of New York (40.74°N) is traveling east at 1,260 km/h (783 mph), at the equator it's moving much quicker, at 1,670 km/h (1,038 mph). Someone in between the two, say on the island of Cuba (21.5°N) will be moving east at 1,554 km/h (966 mph). But here's the crucial thing. In this island dweller's own point of view, the equator is moving east relative to them at 116 km/h (72 mph), but New York actually appears to be going west, at 294 km/h (183 mph). The net result is to set up a turning effect that makes convection cycles, and other cloud masses in the northern hemisphere, swirl in an anti-clockwise direction. And this is why hurricanes and other cyclones spin. The Coriolis effect tends to produce a rising column of warm air that cools and spirals outward at high altitude before it falls back to sea level, gets warmed once more by the ocean and then sucked back to the center where it rises again. As the air rises and cools it releases its heat energy and this is what powers the hurricane.

Creating a sufficient thermal updraft to form a cyclone requires ocean temperatures of over 26°C (80°F). Generally the sea is only this warm within the tropics, which is why cyclones are sometimes known as “tropical cyclones.” Cyclones can form in all the world's equatorial ocean basins. Each area has its own cyclone
season, corresponding to the time of year when the difference between the temperature at sea level and at high altitude is greatest—driving the strongest convection currents. For the North Atlantic, this is June to November with most hurricanes occurring in August and September. In the southern Indian Ocean, the season runs from December until April. Once formed, a cyclone tends to migrate westward, driven by the equatorial trade winds, which blow from east to west. Like hurricanes, the trade winds are caused by a combination of convection and the Coriolis effect. Warm air at the equator rises due to convection, cools and migrates outward to latitudes of +/-30°, where it falls back to sea level. The low pressure that the convection causes then sucks this cooled air back down to the equator where the process repeats. If Earth did not rotate, this air would simply move in a straight line toward the equator, but the Coriolis effect changes that.

Again, it's rather like the situation in a hurricane. Here a patch of low pressure draws air currents radially inwards. But the Coriolis effect makes the currents form a swirling anti-clockwise vortex—in other words, each inward-moving current is deflected to the right. In fact, it's a general tendency of the Coriolis effect in the northern hemisphere to make air currents veer to the right; in the south it makes them veer to the left. And this is what makes the cool air currents heading
toward the equator in the northern and southern hemispheres both veer west to create the trade winds at the equator. These winds blow cyclones in a westerly direction.

Scientists classify the strength of hurricanes on what is known as the Saffir–Simpson scale, first put forward by US engineer Herbert Saffir and US meteorologist Bob Simpson in 1969. The weakest hurricanes are category 1, which have windspeeds between 119–153 km/h (74–95 mph); the strongest hurricanes are category 5, with winds exceeding 250 km/h (155 mph). The center of a hurricane is a region of calm known as the “eye,” which is typically about 50 km (30 miles) across. The air pressure here is low because convection is at its strongest, sucking warm air away from sea level like a vacuum cleaner. The warm, rising air currents spiral up around the edge of the eye forming a thick bank of rapidly rotating cloud called the “eyewall.” It's here that the strongest winds are found and rainfall is at its most torrential.

The strength of a hurricane diminishes rapidly once it reaches land, as its energy source—the warm ocean—disappears from under it. This means that while
coastal regions are especially prone, moving 10–20 km (6–12 miles) inland is often enough to escape the worst effects. That works for saving lives, but what about property damage? After all, there's no way a whole city can be uprooted and moved to safer ground. Is there any way we could influence the physics underpinning a hurricane to alter its course or even stop it in its tracks? One of the earliest efforts to try to change the behavior of hurricanes was the US Project Stormfury, which began in the 1960s. This was an effort to weaken hurricanes by stimulating rainfall within them using a technique called cloud seeding. The idea is for aircraft to fly above the hurricane and drop into it chemical particles with a crystal structure resembling that of ice, such as silver iodide. This encourages water vapor in the storm to cool and condense into clouds, which then fall to the ground as rain. It was believed this would cause the eyewall in a hurricane to get bigger. Just like the spinning ice skater pulls her arms in to go faster and stretches them out to slow down, so windspeed becomes lower as the eyewall gets larger. However, the results of Project Stormfury were inconclusive and it was abandoned.

Recently, US meteorologist Dr. Ross Hoffman has carried out computer simulations showing the effect of heating hurricanes. He found that increasing the temperature at high altitude by just 2–3°C (4–5°F) can have a major effect on a hurricane's course. Heating
the top of the hurricane decreases the vertical temperature gradient, weakening the convection currents that drive it. Hoffman suggests this heating might be achieved using a flotilla of satellites, which could bombard a hurricane with microwaves from above. Another proposal is to disperse soot particles in the hurricane's upper cloud layers. Soot, or indeed anything else black, absorbs heat. Clouds of it in a hurricane's upper decks would absorb sunlight, heating the clouds in much the same way as microwaves. Yet another option is to smother the hurricane in particles of Dyn-O-Gel, a polymer compound that can absorb as much as 1,500 times its own weight in water, soaking up the hurricane's heat-carrying moisture and robbing it of its energy source.