Molten marvel: Mauna Loa’s eruption gives a rare glimpse into Earth

By OLIVER WHANG

NEW YORK: Notice that Mauna Loa, the largest active volcano in the world, was going to erupt — as it did last week for the first time in nearly four decades — came to people on the Big Island of Hawaii an hour before the lava began to flow.

Public officials scrambled to alert nearby residents. Scientists rushed to predict which areas of the island might be in danger. The curious made plans to observe what could shape up to be an event of a lifetime: the exhalation of a massive mountain.

The eruption was years in the making, matched not quite in scale by the ongoing effort to monitor the volcano with seismometers, spectrometers, tiltmeters, GPS units and other state-of-the-art tools.

“Mauna Loa is one of the most well-instrumented volcanoes in the United States,” said Wendy Stovall, a volcanologist with the US Geological Survey.

Even still, so much about the inner workings of the mountain is unknown, Dr Stovall and other scientists said.

Weston Thelen, a volcanologist with the USGS who monitored the mountain from 2011 to 2016, said sheer size, mineral composition and heat all presented logistical difficulties for scientists and public officials hoping to predict its movements. “Mauna Loa is a beast,” he said.

So far the eruption has posed little danger to surrounding communities — and thus has lent a sense of urgency to scientists who are eager to unlock Mauna Loa’s many mysteries.

For how many weeks, months or years will the opportunity remain available?

“Nobody really knows how long this eruption’s going to last,” said Gabi Laske, a geophysicist at the University of California, San Diego. In 1963, a geophysicist named John Tuzo Wilson proposed that the Hawaiian 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 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 the seismometers had provided an X-ray of the magma plume rising beneath Hawaii. 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 behaviour 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.”

Late at night on Sunday, the seismometers around the summit of the volcano started showing more activity. “We’re really trying to understand physically what’s happening in the volcano,” Dr Thelen said.

There’s no knowing when the next eruption will occur. For some volcanologists on the Big Island, this is the first Mauna Loa eruption of their lifetimes. But, as Dr Solomon noted, “on geological time scales, 38 years is pretty short.” Dr Orcutt said: “It’s just something that’s happened for thousands to millions of years, and it’s not going to stop doing that. You can’t hold back the magma forever.”