Photos: Mauna Loa’s Eruption Offers Rare Glimpse Into the Earth

In 1963, a geophysicist named John Tuzo Wilson proposed that the islands, which are covered with layers of volcanic stone, sit above a magma plume, which forms when rock from the deep mantle bubbles up and pools below the crust. This “hot spot” continually pushes toward the surface, sometimes bursting through the tectonic plate, melting and deforming the surrounding rock as it goes. The plate shifts over millions of years while the magma plume stays relatively still, creating new volcanoes atop the plate and leaving inactive ones in their wake. The results are archipelagoes like the Hawaiian-Emperor seamount chain and parts of the Iceland Plateau.

The hot spot theory gained broad consensus in the subsequent decades. “There is no other theory that is able to reconcile so many observations,” said Helge Gonnermann, a volcanologist at Rice University.

Some confirming observations came relatively recently, in the 2000s, after scientists began placing seismometers, which measure terrestrial energy waves, on the ocean floor. John Orcutt, a geophysicist at the University of California, San Diego, who helped lead that research, said that the seismometers had provided an X-ray of the magma plume rising beneath Hawaii. The instruments were able to accurately read the direction and speed of the magma’s flow; the results pointed resoundingly toward the presence of a hot spot.

This hot spot has probably been fomenting volcanic activity for tens of millions of years, although it arrived in its current position under Mauna Loa only about 600,000 years ago. And as long as it remains there, Dr. Orcutt said, it will reliably produce volcanic activity. “Few things on Earth are so predictable,” he added.

Closer to the surface, predicting when, where and how intense these eruptions will be becomes more difficult, despite the profusion of seismometers and satellite sensors. “The deeper you go, the more smooth the behavior gets,” Dr. Orcutt said. “By the time you get this interface between rock and molten rock and the ocean, the magma tends to come out sporadically.”

Under the hood of the volcano