A few weeks back I wrote about how much the lower East Rift Zone of Hawaii’s Kīlauea had been changed by this summer’s eruption. Over half a cubic kilometer of lava came pouring out of the multitude of fissures that opening in Leilani Estates and the neighboring area and 850 acres were added to the Big Island from all those lava flows entering the ocean. It was one of the largest eruptions in the last few centuries at the giant volcano. Yet, the LERZ eruption might not have been the most dramatic change that happened at Kīlauea. To see that, we need to look at what happened at the top.
First, a little background on shield volcanoes like Kīlauea. They are huge edifices and at Hawaii, they rise from the seafloor to a summit that might be hundreds to thousands of meters above sea level. One common feature at the summit of these volcanoes are calderas, which are depressions that are caused by collapses of the land’s surface. Unlike volcanoes such as the ones found in the Andes or Japan, these calderas don’t need to be formed by a massive, explosive eruption — think Crater Lake in Oregon — but rather a gradual collapse. Some of the calderas on Kīlauea were formed by more explosive events, but many weren’t. Barðarbunga the volcano in Iceland that fed the Holuhraun lava field during 2014-15 also experienced one of these gradual caldera collapses, albeit one that was under a sheet of ice.
