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)

Road Trip Adventure- Volcanic Idaho

Continuing on our road trip, this week’s Nature Minute takes us to Idaho’s Craters of the Moon National Monument and Preserve. Located in south central Idaho, the area was once a hotbed of volcanic activity. Ancient lava flows created a unique landscape and habitat. Enjoy this week’s story from the road.

The lava flows that give Craters of the Moon its signature look and name sprang from the Great Rift between 15,000 and 2,000 years ago. The lava beds cover over 1000 square miles, flowing from 25 vents that spewed in at least 8 volcanic events during that time period. Craters of the Moon is the largest of several lava beds in the Great Rift.

Volcanic landscape of Craters of the Moon

Lava in the midground, sagebrush steppe in the
foreground and background

Geological features of the Monument are spatter cones, cinder cones, fissures, lava tubes, and kipukas. The cones and fissures are volcano types. Lava tubes and kipukas are formed by lava movement.

Spatter cones are formed when thick lava is ejected from a volcano. It remains molten when it hits the ground, but due to high viscosity, the blobs of lava do not flow away. Rather, new molten blobs are ejected and they stick together, forming a cone. Cinder cones form similarly, but the lava blobs cool and harden in mid-air, becoming lava bombs (actual geological term). The size and shape of the bombs is dependent on gas content.

Spatter cone (NPS photo)

Fissures are large volcanic cracks in the ground. A full-length fissure eruption is probably the rarest of all volcanic eruptions. Spatter and cinder cones can form in a fissure if it becomes clogged in any area. 

Lava tubes form when the outside of a lava flow cools, forming a hard rock shell. After the remaining molten lava drains, the hollow tube remains. I have been inside a lava tube, the Ape Cave at Mount Saint Helens in Washington.

Lava tube (Oregon State University photo)

Kipukas are islands of older lava flows surrounded by newer lava flows. Vegetation on kipukas is different from the surrounding lava flow areas. At Craters of the Moon, the kipukas are islands of sage steppe surrounded by black lava rock.

Kipuka (NPS photo)

Despite its barren appearance, Craters of the Moon supports a diverse ecological community. Plants include sagebrush, prickly pear, limber pine, and Indian paintbrush. Animals in the Monument include the pika, sage grouse, pygmy rabbits, northern harrier, and common nighthawk.

Limber pine

While visiting, I observed a northern harrier overhead. I took a nice stroll through the Devil’s Orchard, so named by a 19^th century preacher who failed to see beauty in Creation and declared the place to be a garden fit for the devil. I enjoyed seeing the lichen that are working around the clock to turn rock into soil so larger plants can colonize. The twisted branches of the limber pine, knotted by mistletoe, set against a stark black backdrop made for an eerie sight. I enjoyed my brief visit and would like to return for a more in-depth look around. I chose not to linger because Craters of the Moon was the undercard for the main even, Yellowstone.

Limber pine with "witch's brooms"

Polished lava rock with swirls

Hardened slow-moving lava flow

Information this week comes from the National Park Service about kipukas, including the picture above. Great Rift information comes from a paper by the folks at Idaho State University. Photo credits go to National Park Service (spatter cone) and Oregon State University (lava tube). All others are my own.