Hell's Half Acre

Overview

Hell's Half Acre Lava Trail traverses the desert ecosystem of the Snake River Plain through rough terrain, unusual scenery, and contorted landscapes created from multiple lava flows. Most of the calderas left behind by the violent eruptions of the Yellowstone hotspot have been buried by many less violent, Hawaii-type lava flows associated with the stretching of the Basin and Range. The most recent flow in eastern Idaho is the Hell's Half Acre lava flow which erupted about 4,100 years ago and is 125 square miles. The lava that flowed in these basaltic eruptions was probably about 2,000 degrees Fahrenheit, the consistency of molasses, and traveling at speeds up to 30 mph.

Hell's Half Acre is designated as a National Natural Landmark (NNL) and a Wilderness Study Area (WSA). These designations help preserve the area so the public can enjoy and study this unique geologic area in its healthy, natural condition. The Lava Trail System is open to non-motorized recreation activities only.

Hiking across the lava is a unique experience. Lava rock is extremely sharp, glassy and fragmented, with open cracks, lava tubes and caves. The most prevalent landscape consists of A'a (ah-ah) and Pahoehoe (pa-hoy-hoy) lava flows. Pahoehoe lava is more fluid than A'a. It's outer surface cooled faster than the interior causing a "ropey" appearance. The less fluid A'a formed leaving rough, irregular mounds. The areas of soil and vegetation not covered by lava area called "kipuka," a hawaiian word meaning 'window in the lava.'

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