Where the Clouds Roll By
Where the Snow Is Like Knives
These sharp snow formations make the white stuff look uninviting. They’re called penitentes, and although they can form at high altitudes anywhere, there’s no place better to see them than in the Dry Andes of Chile and Argentina, way up past 13,000 feet (about 4,000 meters).
Penitentes, named after pointy hats worn by people doing penance for their sins in Christian traditions, form in very cold, dry air, where the water in snow sublimates, or turns directly into vapor without melting first. Sublimation randomly occurs faster in some areas than in others; once uneven pock-marks form in the snow, they focus the sunlight, causing those areas to sublimate ever faster. Spiky penitentes get left behind, unmelted. The tallest penitentes can reach 12 feet (4 meters) high.
Where the Lakes Explode
To see a lake that can kill you without you even dipping in a toe, visit Africa. In Cameroon and on the border of Rwanda and the Democratic Republic of the Congo are three deadly lakes: Nyos, Monoun and Kivu. All three are crater lakes that sit above volcanic earth. Magma below the surface releases carbon dioxide into the lakes, resulting in a deep, carbon dioxide-rich layer right above the lakebed.
In 1984, Lake Monoun abruptly exploded, releasing waves of water and a cloud of carbon dioxide. Thirty-seven people who lived near the lake asphyxiated in the CO2 cloud, though the cause of their deaths remained a mystery until two years later, when Lake Nyos let out its own burst of carbon dioxide. This time, 1,700 people died when the carbon dioxide, which is heavier than oxygen, displaced the breathable air in their villages.
Venting pipes have been installed in Lake Nyos and Lake Monoun in an attempt to release the carbon dioxide gas slowly and prevent future disasters. Kivu, which has never erupted, is not being vented, although local companies do extract dissolved methane from the lake to use for power generation.
Where Tsunamis Sweep Mountains
In landlocked Bhutan, tsunamis are becoming a danger. Climate change is melting Himalayan glaciers, increasing the risk that glacial melt will break through ice dams and wipe out villages. Scientists call these flash floods, one of which killed dozens in 1994, "glacial-lake-outburst floods," but in layman's terms, they're mountain tsunamis.
Bhutan is working to ease the danger by draining some high glacial lakes and shoring up their natural dams. Glacial lake outbursts can happen anywhere where glaciers are melting, but according to Bhutan's government and the United Nations, 24 of the country's 2,674 glacial lakes are at risk, making Bhutan the epicenter of this phenomenon. [Ice World: Gallery of Awe-Inspiring Glaciers]
Where the Rocks Walk
At Racetrack Playa in Death Valley, it’s not horses or stock cars that make the rounds — it’s rocks. This pancake-flat dry lakebed is marked by tracks of large rocks that seem to have wandered from here to there under their own power.
In fact, the rocks (some of which weigh tens or hundreds of pounds) may require a perfect storm to get moving. According to lunar and planetary sciences researchers at NASA Goddard, wind pushes the rocks around. But for the wind to move huge boulders, there has to be little friction between the rock and the ground. Most likely, ice-encrusted rocks get inundated by meltwater from the hills above the playa, according to NASA researchers. When everything’s nice and slick, a stiff breeze kicks up, and whoosh, the rock is off.
Where Crystals Dwarf Humans
Imagine an underground world where shimmering crystals crisscross caverns like a giant’s Tinkertoys. Mexico's Cave of Crystals, buried below the Chihuahuan desert, is just that. Here, enormous crystals of selenite grow more than 30 feet (10 meters) long.
But this fantasy world is tough to withstand. The cave is nearly 1,000 feet (300 meters) below the surface, and a magma chamber below keeps the caverns heated to about 136 degrees Fahrenheit (58 degrees Celsius), with 99 percent humidity. Explorers must wear protective gear if they hope to survive in this crystal cave for more than a few minutes. [Amazing Caves: Pictures of the Earth's Innards]