Despite some clues suggesting speedy magma ascents, most models of volcano plumbing were akin to a slow pipe. A volcano's magma chamber fills from the bottom, like a sink filling from its drain. Many pulses of molten rock can pump into the chamber during a volcano's lifetime. Based on geochemical evidence in lava, researchers thought the magma melts would rise a bit, mix together, and then climb a little more, until finally reaching the chamber. The long journey happens over a span of thousands to hundreds of thousands of years.
"It's like going up a set of stairs. Each step is another change," said Adam Kent, a geologist at Oregon State University who was not involved in the study. "By the time you get to the surface, the magma has been changed quite substantially."
But the new study found evidence that magma feeding the 1963 eruption skipped the stairs and took the express elevator to the surface, mixing with other molten rock only at shallow depths, around 6 miles (10 kilometers) below the Earth's surface.
"This is telling us some interesting stuff about what's driving these volcanoes, which is hot stuff coming from deep within the mantle," Kent told LiveScience's OurAmazingPlanet. "The real proof of the pudding would be to find this behavior at many different places," he said.