# Volcano Watch — Idaho's Craters of the Moon shares similar traits with Kīlauea

June 14, 2007

One of the most fascinating things about living on, or visiting, the Big Island is our proximity to active volcanoes and the wide variety of associated volcanic features and products. Nearly every road cut reveals Hawaii's volcanic past, and we do not have to travel far before crossing the treeless expanse of a recent lava flow.

But Hawaii is not the only place in the United States where we can explore basaltic lava fields with shield volcanoes, lava tubes, cinder cones, and the like. Scattered across the western U.S. are dozens of young lava fields, each of which is characterized by features and products very similar to those found here in Hawaii. The largest of these is the Craters of the Moon lava field, covering 1,600 square kilometers (618 square miles) of south-central Idaho. This is also the name of the National Monument, administered by the National Park Service, that encapsulates the lava field.

Craters of the Moon is located on the eastern portion of the Snake River Plain, which is a 50- to 100-kilometer-wide (30- to 60-mile-wide) topographic low in southern Idaho that extends some 360 kilometers (600 miles) from Oregon to the Yellowstone Plateau in northwestern Wyoming.

The younger, eastern portion of the Snake River Plain is composed of an estimated 8,000 shield volcanoes, each of which erupted about 5 to 21 cubic kilometers (1.2 to 5 cubic miles) of lava. These are very small volcanoes compared to those found here in Hawaii. For example, Kīlauea, in its current eruption, has already spit out about 3.1 cubic km (0.7 cubic miles) of lava since 1983. This past week, activity levels at the summit of Kīlauea Volcano have remained elevated, but may be returning to background levels. Earthquakes continue to be concentrated in the upper southwest and east rift zones. The summit caldera has been expanding, indicating inflation, since the early 2007.

Like Hawaii, volcanism on the Snake River Plain is related to a "hotspot"—a place where excess heat rises from the earth's mantle to melt the overlying crustal rocks. In this case, the hot spot in question is now beneath Yellowstone. The eastward progression of the Yellowstone hot spot across Idaho is traced by the Snake River Plain.

The Snake River Plain also happens to sit in the middle of what is called the Basin and Range Province, where extensional forces are slowly tearing the North American continent apart. It is thought that crustal decompression, related to this extension, allows partially melted rocks—left over from when Yellowstone passed by—to erupt at the surface.

The Craters of the Moon lava field is composed of over 60 separate lava flows that were erupted between 15,000 and 2,100 years ago. The vents that supplied the lava are aligned along the northern end of an 85-km-long (53-mile-long) extensional crack called the Great Rift. Two other lava fields of comparable age—the King's Bowl and Wapi lava fields—were erupted from the southern end of the same crack.

The volcanic features at Craters of the Moon are typical of basaltic volcanism. There are, for example, some 25 cinder cones at Craters of the Moon that, like Hawaii, formed during episodes of lava fountaining. Big Cinder Butte, the highest of these cones, stands 250 m (820 ft) above the surrounding plain and has a total volume of about 0.2 cubic kilometers (0.05 cubic miles). It is similar to Puu Oo, the cinder cone formed early (1983-1986) in Kīlauea's current eruption. At its maximum, Puu Oo stood 255 m (837 ft) high and had a volume of about 0.14 cubic kilometers (0.03 cubic miles).

The lava flows at Craters of the Moon, like the ones in Hawaii, were tube-fed—the flows formed lava tubes, insulating the molten lava and enabling it to be transported kilometers (miles) away from the erupting vents.

The last eruption at Craters of the Moon ended some 2,100 years ago and was likely witnessed by the locals. The Shoshone people, who lived in the area at the time, tell of a serpent on a mountain who, when angered by lightening, coiled around his domain. The serpent squeezed until liquid rock flowed, and the mountain exploded. Geologically speaking, 2,100 years is but a blink of the eye, and Craters of the Moon may have more eruptions in store. The legendary serpent may someday return to squeeze the mountain again.

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### Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have remained elevated, but may be returning to background levels. Earthquakes continue to be concentrated in the upper southwest and east rift zones. The summit caldera has been expanding, indicating inflation, since the early 2007.

The eruptive activity at Puu Oo continues. On clear nights, glow can be seen reflected in the gas plume above vents on the eastern half of the crater floor. The lava that is erupted onto the surface, however, comes from the PKK vent on the southwest flank of Puu Oo and flows directly into the PKK tube.

A breakout from an old skylight about 450 meters (1500 feet) below the head of the PKK tube has been sending lava down slope since mid-May. This new flow, called the Petunia flow, surged forward in the last few weeks and, as of June 13, was just above the top of Pulama pali. The flow may soon crest over the top of the pali to the west of the Campout flow and become visible from the end of the Chain of Craters road in the National Park.

The Campout tube, which branches off from the PKK tube below the Petunia tube, continues to carry lava downslope. The original PKK lava tube is no longer active below the Campout tube branch. The Campout flow continues to feed small breakouts scattered across the coastal plain from near the base of the Royal Gardens subdivision to the sole ocean entry at Poupou. The number of surface breakouts inland from the entry, however, has declined over the last few weeks. The Poupou entry, which is located within Hawaii Volcanoes National Park, has two closely spaced entry points, each producing a robust plume. Despite a sizeable volume of lava entering the ocean, the lava delta remains relatively small.

Access to the sea cliff at the ocean entry is closed, due to significant hazards. The surrounding area within Hawaii Volcanoes National Park, however, is open. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water and wear good shoes when venturing out onto the flow field.

Two earthquakes beneath Hawaii Island were reported felt within the past week. A magnitude-2.6 earthquake occurred at 11:24 p.m. H.s.t. on Tuesday, June 12, and was located 26 km (16 miles) west of Waikoloa Village at a depth of 38 km (24 miles). A magnitude-3.5 earthquake occurred at 4:39 a.m. on Thursday, June 14, and was located 7 km (4 miles) southwest of Puu O`o crater at a depth of 10 km (6 miles).

Mauna Loa is not erupting. One earthquake was located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates.