Describe the type of volcano that is being studied in this article. How does it behave? What extinct (hopefully!) volcano closer to home might erupt the same way?

An Icelandic Volcano Reveals Secrets of Its Eruption By HENRY FOUNTAIN JULY 14, 2016 A plane flying over the Bardarbunga volcano spewing lava and smoke on Sep. 14, 2014. C redit Bernard Meric/Agence France -Presse — Getty Images Some of the world’s most cataclysmic volcanic eruptions are associated with the collapse of a caldera, a depression in the top of the volcano that forms and deepens as a reservoir of magma below it e mpties out. The two largest of the 20th century — Pinatubo in 1991 in the Philippines and Novarupta in Alaska that formed the spectacular Valley of Ten Thousand Smokes in 1912 — both blew their tops this way. Caldera collapses are rare, and when they do occur they usually happen quickly, in hours or a few d ays. But when Bardarbunga , a large volcano under an ice cap in central Iceland, erupted in August 2014, the caldera sank and collapsed gradually over the course of the six -month eruption. That gave scientists a unique opportunity to study it. In a report published Thursday in the journal Science, volcanologists reveal that the sinking caldera actually helped drive the eruption, by keeping pressure on the magma chamber as the hot rock flowed out. “We are talking about a hydraulic system,” said Magnus T. Gu dmundsson, a researcher at the University of Iceland and lead author of the paper. The caldera, he said, pushed down on the reservoir of magma, which flowed nearly 30 miles through a fracture in the volcano before emerging at the Holuhraun lava field . Because the caldera collapse happened under the Vatnajokull ice cap, which is about 1,500 feet thick on average, Dr. Gudmu ndsson and his colleagues had to study it indirectly using seismometers, radar and other instruments. They also placed GPS sensors on top of the ice, which enabled them to gauge the collapse of the caldera because the ice followed it as it sank. The calder a is roughly oval in shape, covering about 40 square miles, making the collapse the largest ever monitored. Over the course of the eruption it sank about 200 feet. Every week, we'll bring you stories that capture the wonders of the human body, nature and t he cosmos. Dr. Gudmundsson said the research showed that the eruption started when pressure increased within the magma chamber, which is at a depth of about seven miles. The caldera collapse began about five days later, when an estimated 12 percent to 20 p ercent of the magma had already left the chamber. If the collapse had not started, Dr. Gudmundsson said, the eruption might have ended at that point because the loss of all that magma had reduced the pressure in the chamber. But the collapse put new pressu re on the chamber, and the flow of lava continued. The caldera, he said, “is like a piston pushing down on a body of fluid, and there is a pipe going from this container of fluid sideways to the surface.” John Stix, a volcanologist at McGill University in Montreal, said the Bardarbunga findings were fascinating for what they showed about the mechanics of the collapse. “One would think that calderas don’t collapse like pistons,” he said. “But effectively that’s what’s happening.” He said the study would help scientists better understand what drives extremely large eruptions like Tambora in what is now Indonesia, which led to what became known as the “year without a summer” when it erupted in 1815. Dr. Gudmundsson noted that scientists did not notice that the Bardarbunga caldera was collapsing until about two weeks after it st arted. That would not happen today, he said, thanks to this research, which identified the kinds of seismic signals that indicate the start of a collapse. “That’s very important to know,” Dr. Gudmundsson added, “because not all collapses are as gradual and well behaved as this one.” For instance, if Yellowstone were to erupt again it would no doubt involve a collapsing caldera and be far more catastrophic than the one observed in Iceland. Despite some of the hysteria about Yellowstone, which last erupted 640,000 years ago, the odds of another eruption happening any time soon are vanishingly small .