Mount St. Helens is rumbling again, reminding everyone what happened when the volcano erupted in 1980. (It killed 57 people, and flattened some 10 million trees.)
The threat is serious. Humans have learned the hard way that, when you see smoke pouring from the top of a nearby mountain, get moving and don't look back.
Top 5 Ways Volcanoes Can Kill You
In the movies, volcanoes kill people by raining lava down on them or by cutting off escape routes with pools of molten rock. But real-life volcanoes don't need to resort to such theatrics. They have more effective ways to do you in.
1. Pyroclastic Flow
This deadly mixture of superheated volcanic gas, ash, and rock rushes down the face of the volcano as fast as 100 miles per hour (160 km/h). With temperatures up to 1,300° Fahrenheit (700° C), the cloud can obliterate buildings, incinerate obstacles, and kill any creature in its path.
Where it happened: In A.D. 79, Mount Vesuvius in Italy buried the town of Pompeii with ash and pumice. Several thousand people suffocated in a cloud of red-hot ash and poisonous gas. The ash settled around their bodies and set as hard as concrete, preserving the space they had occupied. Archaeologists were able to make strikingly lifelike plaster casts of bodies that had crumbled to dust 2,000 years before.
2. Tsunami
These cataclysmic waves are often called tidal waves, but that's not really correct--they have nothing to do with tides. Tsunamis are formed by seismic phenomena such as earthquakes and volcanoes. By the time a tsunami approaches the shore, the wave that was hardly noticeable when it formed out at sea is huge.
Where it happened: When Krakatoa erupted in 1883, it created one of the most catastrophic natural disasters in human history. The explosion on the Indonesian volcanic island was so great that the boom could be heard thousands of miles away. Ash shot 50 miles (80 km) in the air and so much material was expelled that most of the island collapsed into the sea, triggering a tsunami that smashed into coastal towns in Java and Sumatra and left 36,000 people dead.
3. Lahar
These mudflows of volcanic material flow with such force that they can carry large boulders at high speeds for many miles. Obstacles in the lahar's path are typically battered, broken, and buried in mud.
Where it happened: Less than twenty years ago, Nevado del Ruiz in Colombia blasted molten rock outward, which melted the mountain's cap of ice and snow. A wall of water, mud, and ash raced down the mountain. Just before midnight on November 13, 1985, what looked like a river of wet concrete buried the town= of Armero, killing 23,000 people.
4. Landslide
Avalanches are common on volcanoes, where there's a lot of loosely packed rock and ash, seismic trembling, and a mountain that might be getting steeper by the minute. Tremors trigger the slide, which can have deadly effects.
Where it happened: The worst volcanic disaster in Japan's history occurred at Mount Unzen in 1792. After spewing some lava, the volcano went silent for a month. Then a lava dome collapsed, causing a landslide that ripped through Shimabara City. The debris crashed into the sea and generated a tsunami that devastated the coast. In the end, as many as 15,000 people were dead.
5. Gas
Volcanoes belch gases from deep inside the Earth. Some of them just smell bad, but others kill. Sulfur dioxide and carbon dioxide are just two of the noxious gases that seep from vents in the Earth's crust.
Where it happened: Volcanic activity in the African nation of Cameroon in 1986 caused a huge amount of carbon dioxide to spurt up through Lake Nyos and reach a deadly concentration. The suffocating cloud drifted over nearby villages and killed 1,700 people, most as they slept.
And After All That, You Starve
Once the eruption is over, your problems might be just beginning. The release of ash and poisonous gases can choke vegetation and spoil fresh water sources. The next thing you know, your crops have failed and your livestock are dying. An eruption that directly kills a thousand people might leave tens of thousands dead from famine and disease in the months that follow.
Where it happened: Mount Laki in Iceland erupted for more than eight months in 1783 and 1784, hurling lava over 220 square miles (565 square km). The gases stunted crops and grasses and killed most of the island's domesticated animals. More than 9,300 people--one-fifth of Iceland's population--perished during the resulting famine.
Want to learn more?
Explore the geologic causes of an eruption
http://www.geolo= gy.sdsu.edu/how_volcanoes_work
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