The Floor is Lava!

The Kilauea eruption in Hawaii has been making headlines recently, with hundreds of residents displaced on the Big Island. Let’s take a look at what’s happening there and why.

Volcanoes are vents into the center of the earth. Liquid hot magma in the mantle is forced upward to the crust by pressure. Once in a while, the pressure is great enough to force the magma out of the ground. We call it a volcanic eruption, and change the magma’s name to lava. Not all eruptions produce lava; in many cases gases and rocks are thrown from the volcano. Such was the case at Mount St. Helens in 1980 and 2004. This particular eruption isn’t even centered on the volcano’s summit crater. While there have been steam, ash, and rocks erupting from the summit crater, there hasn’t been a lava eruption there yet. Much of the lava is spewing from fissures, cracks that have opened in the ground.

Kilauea summit crater, May 9, 2018 (USGS)

 

Fissure eruption, Jan 3, 1983 (USGS)

Most of the world’s active volcanoes are at the edges of tectonic plates. To understand the concept of plates as they relate to volcanic activity, imagine the crust is thin pieces of rocks fit together and floating on top of the liquid magma mantle. The plates fit together but not tightly enough to keep some of the magma from oozing to the surface. In some areas, one plate is sliding underneath another. An example is the Juan de Fuca plate sliding under the North American plate in the Pacific Northwest. This action created the volcanoes of the Cascade Range. In other areas, the plates are pulling away from each other, as in the Mid-Atlantic Rift. The Eurasian and North American plates are separating, and the material coming forth from the seafloor is what gave us Iceland.

Map of the world's tectonic plates. The Ring of Fire
flanks the west coast of the Americas and east coast of Asia.
(Science Education Resource Center)

Ring of Fire volcanoes in Oregon (Universities Space Research Association)

Hawaii is in the middle of the Pacific Ocean, thousands of miles from the edge of the Pacific plate. Why the volcanic activity then? Hawaii sits on top of a hot spot. The hot spot is a leak in the ocean crust. The Big Island is the newest in the Hawaiian chain, and still growing as we can see. The hot spot has been leaking magma into lava for millions of years. The spot remains in place, while the plate slides along above it. That’s why Hawaii is a series of islands. The plate is moving to the northwest, so the islands are oriented from northwest to southeast. The current situation in Hawaii is even happening on the southeast side of the island. As time goes by, activity at Kilauea will cease and a new island will rise southeast of Hawaii.

Hawaiian hotspot (Smithsonian Institution)