At first the lava is very fluid and charged with gas. Eruptions begin as a long line of fountains that reach heights of 1,000 feet or less and are up to a mile in length. This “curtain of fire eruption” mainly produces cinders and frothy, fluid lava. After hours or days, the expansion of gases decreases and eruptions become less violent. Segments of the fissure seal off and eruptions become smaller and more localized. Cinders thrown up in the air now build piles around individual vents and form cinder cones.
With further reductions in the gas content of the magma, the volcanic activity again changes. Huge outpourings of lava are pumped out of the various fissures or the vents of cinder cones and form lava flows. Lava flows may form over periods of months or possibly a few years. Long-term eruptions of lava flows from a single vent become the source of most of the material produced during a sustained eruption. As gas pressure falls and magma is depleted, flows subside. Finally, all activity stops.
When Will the Next Eruption Occur? Craters of the Moon is not an extinct volcanic area. It is merely in a dormant stage of its eruptive sequence. By dating the lava flow, geologists have shown that the volcanic activity along the Great Rift has been persistent over the last 15,000 years, occurring approximately every 2,000 years. Because the last eruptions took place about 2,000 years ago, geologists believe that eruptions are due here again—probably within the next 1,000 years.
From the air the Great Rift looks like an irregularly dashed line punctuated by tell-tale cones and craters.
Chainlike, the Hawaiian group of islands traces the migration of Earth’s crustal plate over an unusual undersea heat source. The Hawaiian chain of islands and the Snake River Plain map similar happenings.
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Indian Tunnel
