Mental Floss

Phreatic explosions and lava bombs

Ransom Riggs

A few months ago, I took a really cool trip out to Death Valley -- check out my posts on the mysterious moving rocks of Racetrack Playa, the world's toughest footrace and scenic pioneer graves -- but since it's no longer very cool in Death Valley (Saturday's high will be 114 fahrenheit), what I learn about California's Great Basin treasure will have to be sourced from the internet. As it happens, there's one fascinating site I neglected to mention: Ubehebe Crater. Measuring about 800 feet across and 700 feet deep, it's a blast crater created by volcanic activity, to be sure, but this wasn't your typical volcanic explosion. It was a phreatic eruption -- a particularly deadly variety.

Phreatic eruptions happen when magma flows close to the surface, and comes into contact with groundwater. The magma is unbelievably hot -- up to 2,100 degrees F -- and turns the water instantly into steam, resulting in a lava-less but extremely destructive explosion which can include "volcanic bombs" (huge blobs of magma that cool into solid rocks before they hit the ground), great quantities of carbon dioxide (which can suffocate people at sufficient concentration) and hydrogen sulfide gas (a broad spectrum poison which claimed 149 lives during a 1979 eruption in Java). The phreatic eruption hall of fame is a storied one, and includes such volcanic superstars as the 1980 eruption(s) of Mt. Saint Helens and the "loudest sound in human history," the eruption of Krakatoa in 1883 (which we blogged about here). In short, it seems that the heat isn't the only reason they call it Death Valley.