5 Natural Disasters Headed for the United States
By Jim Gorman
Source: http://www.popularmechanics.com

Earth is one rough place. Even the most devastating storms of recent years pale in sheer destructive power against outsize natural disasters of the past, such as continent-smothering ice sheets, ocean-raising floods, super volcanoes and the occasional asteroid. Because cataclysms will always be a regular feature of life on Earth, PM consulted with leading scientists to detail five more disasters that may be in store. Some will be beyond human control; others could be disasters of our own making. Either way, prepare for a real doozy.

40-Mile-Long Mudslide, Washington State
Movin' Mountain
On an overcast afternoon high on Mount Rainier, a rocky slope slumps and then cuts loose from the mountain. Small rock slides are common on the volcano's steep flanks, but this one is different. Most of Mount Rainier's west face is in motion. Into the tumbling maelstrom go millions of tons of ice from the Puyallup and Tahoma glaciers. House-size rocks disintegrate in the downward crush. “With Rainier's active hydrothermal system saturating the rock, the landslide would reach the base of the slope as a flowing mass of watery, muddy debris,” says Kevin Scott, scientist emeritus at the U.S. Geological Survey's Cascade Volcano Observatory (CVO).

So a lahar is born--a volcanic mudflow--and a nightmare realized for the approximately 150,000 Washington residents who live and work on the solidified debris of past flows. The mass of roiling mud, rock and trees, traveling at 60 mph, would quickly funnel into the canyons of the Puyallup and Carbon rivers, where it would rise 180 ft. high before spreading into the lowlands as a 15-ft. wave. The 5000 residents of Orting, at the rivers' confluence, would have less than 45 minutes to evacuate. People downstream, in towns such as Puyallup and Sumner, might have twice that long.

Despite its iconic standing, 14,410-ft. Mount Rainier is pocked with corroded, unstable rock capped by a cubic mile of ice and snow. The mountain--weakened from the inside out by acids resulting from upwelling magma--has partially collapsed many times in the last 5600 years, unleashing mudflows that have inundated five of six major drainages. Six of those lahars surged at least 45 miles to reach Puget Sound.

The USGS gives a 1-in-7 chance of a similar event occurring in anyone's lifetime. And, says Dan Dzurisin, a CVO geologist: “There's no guarantee there would be any advance warning.”

80-Ft.-High Tsunami, Atlantic Coast
Coast Buster

A massive collapse of Cumbre Vieja in the Canary Islands would cause a tsunami to radiate all the way across the Atlantic Ocean to the East Coast. PHOTOGRAPH BY J. SCHWAKE/ALAMY

Cumbre Vieja, the most active volcano in the Canary Islands, lurches as a violent earthquake wracks its upper slopes. A third of the mountain breaks away and plunges into the Atlantic Ocean, pushing up a dome of water nearly 3000 ft. high. They don't yet know it, but tens of millions of Americans from Key West, Fla., to South Lubec, Maine, have just 9 hours to escape with their lives.

The collapse of Cumbre Vieja unleashes a train of enormous waves traveling at jetliner speed. The first slam into nearby islands, then the African mainland. By the time they reach the East Coast of North America, the waves are up to 80 ft. high, and in low-lying areas, sweep several miles inland.

When tsunamis strike the United States, it is usually Hawaii or Alaska that take the hit. But topography and population density put the East Coast in a special risk category. “More Easterners are exposed to potential tsunamis--from the Canary Islands or the Cape Verde Islands--than the people on the West Coast, which has a steep coastline and few lowlands,” says Steven Ward, a geophysicist at the University of California, Santa Cruz. A Cumbre Vieja eruption in 1949 opened a mile-long, 20-ft.-deep fissure near the crest, forcing the volcano's western face to slump several feet. A 1971 eruption didn't budge it.

Marine geologists at Southampton Oceanography Center in Great Britain have a different take. They conclude the volcano would collapse in stages-- at worst threatening nearby islands. Ward calculates only a 5 percent chance Cumbre Vieja will trigger a tsunami in a given century, but that when it does a chunk of earth 15 miles long, 9 miles wide and nearly 1 mile thick will plunge into the sea--a landslide 250 times larger than the collapse of Mount St. Helens.

The tsunami's probable trajectory within 5 hours of the collapse of Cumbre Vieja.

The tsunami's potential range of destruction 9 hours after the collapse of Cumbre Vieja

Magnitude 6.9 Earthquake, Mississippi River Valley
Stress Test

The New Madrid Seismic Zone, which extends into five states, is part of a rift that formed more than 500 million years ago when tectonic forces began pulling the continent apart.

Ten miles beneath Caruthersville, Mo., stress along an ancient rift zone releases in a violent spasm. Shock waves from the magnitude 6.9 earthquake roll 160 miles up the Mississippi River Valley to St. Louis, and 75 miles downriver to Memphis, Tenn. The soils under Memphis ripple like a shook rug. Century-old brick buildings heave, then crumble. Sewer and water lines rupture. Gaslines snap. Downtown, the 14-story federal building, a decade overdue for quakeproofing, rains 3-ton panels.

While all eyes are fixed on California as the site of the next “Big One,” damage from a quake along the New Madrid Fault--which runs for 150 miles between Marked Tree, Ark., and Cairo, Ill.--may be greater. The hot, shattered crust beneath California absorbs seismic energy quickly and focuses it at an epicenter, says Gary Patterson, a geologist at the University of Memphis. But, he says, “the relatively hard, cold slab of rock beneath the central U.S. allows that energy to travel great distances.” A quake's impact zone is at least 10 times larger on the New Madrid Fault than on the San Andreas, and its shock waves reverberate longer.

The New Madrid Fault has produced the strongest earthquakes in the contiguous states: three tremors near magnitude 8.0 that struck from December 1811 to February 1812. Odds of a quake of that scale are small: 7 to 10 percent in the next 50 years. But factor in unprepared citizens and infrastructure and even a 6.0 earthquake, which has a 25 to 40 percent chance of occurring, would be a disaster.

“There's a lot about the New Madrid we don't know,” Patterson says. “But what we do know is very concerning.”

195-MPH Hurricane, Florida
Tropical Terror
Packing maximum sustained winds of 195 mph, Hurricane Lyle slams into Coral Gables just south of Miami. The breadth and intensity of the storm dazzles meteorologists, who rank it the strongest hurricane ever to hit the U.S. mainland.

On the north side of the storm's eye, Miami Beach, which has the second highest housing density in the country, is in shambles. Many residents don't evacuate, believing they are safe in concrete high-rises. They are wrong. Then it is too late, as the causeways connecting them to the mainland wash out. Waves riding a 15-ft. storm surge gut oceanfront condos up to the third story; windows blow out, allowing wind and rain to ravage upper floors. The storm surge sweeps over the island, carrying wreckage into downtown Miami, where the 70-story Four Seasons Hotel and Tower is reduced to a sodden shell.

Low-lying coastal areas would be hit twice by a supercharged storm—as waves rushed in and then back out. PHOTORAPH BY WARREN FAIDLEY/CORBIS

Block after block of homes in Coral Gables, West Miami and Sweetwater--many not yet retrofitted to the tough codes imposed after Hurricane Andrew in 1992--are blasted down to roofless frames. Waist-deep floodwater inundates areas as far north as Fort Lauderdale. Insured losses exceed $100 billion--nearly twice the amount caused by Katrina--making Lyle the costliest natural disaster in U.S. history.

Katrina should have been a wakeup call, but coastal development has continued unabated, exposing the 4 million people in Florida's Miami-Dade and Broward counties to deadly monster storms. Warm water is rocket fuel for hurricanes, and global warming is predicted to heat tropical oceans by 4 F in the next century. Sea surface temperatures in the tropics have already risen by about 1 F since 1970.

Researchers at Georgia Tech and at the National Center for Atmospheric Research in Boulder, Colo., have measured a near doubling in the annual number of Category 4 and 5 storms during the past 35 years. And Kerry Emanuel, professor of meteorology at MIT, has found that Atlantic storms today wield twice the destructive force as those in 1970.

Wind speeds increase with altitude, and so a Category 4 storm at ground level can be a full category higher at the top of a building. While the storm surge scours the first two stories, overpressure blows out windows in the highest floors, exposing the interiors to wind and rain.

Some scientists dispute the global warming-hurricane connection. They attribute the intensity of recent hurricanes to natural cycles, or they contest the accuracy of early data and the objectivity of techniques used to analyze it.

Supercharged or not, hurricanes promise to wreak unprecedented damage in the decades ahead for one simple reason: More people have put themselves in harm's way. Coastal zones from Texas to North Carolina have gained 24 million residents since 1950.

Climate-Changing Ocean Disruption, North Atlantic
Sea Change
Winters in the Northeast begin to bite with a ferocity last seen during the deep freezes of 1936 and 1978, when icebreakers plied the Mississippi and Hudson rivers. Winter temperatures in Washington, D.C., begin to approximate those of Boston. Extreme drought grips the Midwest, sending grain commodity prices soaring; crops fail and farmers spin into bankruptcy. Climate patterns go haywire. London, Paris and the Scandinavian capitals shiver through their coldest winters since 1850. Summer monsoons in India and China weaken, affecting harvests that feed hundreds of millions of people. Fisheries decline when plankton populations collapse. Drought and flood push worldwide agricultural losses to $250 billion.

The cause of the big chill is an unlikely culprit: global warming. The northeastern States, eastern Canada and, primarily, Europe enjoy warmer climates than they otherwise would because of an ocean-based system of heat delivery called thermohaline circulation. This vast ocean conveyor sweeps warm, salty water from tropical latitudes north along the surface. After shedding heat to the atmosphere, the chilled brine becomes denser and sinks. Thousands of feet beneath the surface it flows back toward the equator, completing the loop.

Freshwater melt from the Greenland ice sheet contributes to a layer of buoyant water that is beginning to cap the North Atlantic Ocean. PHOTOGRAPH BY BLICKWINKEL/ALAMY

But as the climate warms disproportionately at the poles, the gears of the system begin to wobble. Freshwater runoff from Greenland's ice cap and from melting glaciers across the Arctic, combined with increased precipitation, could form a thick, buoyant cap over the North Atlantic. Already, the great gyre may be sputtering. The surface of the North Atlantic is becoming noticeably less salty, and thus less driven to sink.

Thermohaline circulation shut down as recently as 8200 years ago, and some scientists contend that the Little Ice Age of 1300 to 1850 was due to a hiccup in the system. The chance of another collapse is hotly debated. Terrence Joyce, a senior scientist at Woods Hole Oceanographic Institution, calls it “unlikely” if Greenland's ice cap continues to melt at the current pace. However, “Greenland is a wild card,” he says--its melt rate remains unpredictable. Michael Schlesinger, an atmospheric scientist at the University of Illinois, Urbana-Champaign, calculates a 45 percent chance of the system shutting down in the next century if nothing is done to slow global warming.

Cold, dense water typically sinks near the Arctic and flows in deep currents to the equator. When this cycle is disrupted, warm water is not pushed as far north along the surface.

Ice core samples indicate the switch from temperate to bitter could be measured in mere years--and last for centuries. The timing of such an event will determine the severity of its consequences. “If the shutdown happens 100 years from now, it will bring us back to where we are now, canceling 4 to 6 F of atmospheric warming [predicted] in the Northeast,” Joyce says. “If it happened tomorrow, that would be something more significant.”