Before Kilauea’s recent outburst, Alex had often visited the Halema‘uma‘u [HAH-lay-maohmaoh] crater at the volcano’s summit (see Understanding Kilauea). From there, he could see the crater’s lava lake. But last April, the lake overflowed onto the crater floor.
Around the same time, ground instruments and satellite images revealed the swelling of land around Pu‘u ‘O‘o [POO-oo OH-oh]—a vent, or opening, farther downslope that contained another lava lake. “We were literally seeing the ground inflate,” says Mandeville.
The changes people were witnessing were caused by underground molten rock, called magma, flowing upward into the volcano faster than it could be released aboveground as lava. “We knew that eventually the system would bust open, but we didn’t know where,” says USGS volcanologist Wendy Stovall.