Hell's Half Acre

Geography & Climate

Hell's Half Acre is located in United States, within the Yellowstone-Snake River Hotspot Volcano Group of the broader North America Volcanic Regions. Situated at 43.49° N, 112.45° W in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 1,632 meters above sea level, Hell's Half Acre is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a shield, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Hell's Half Acre is situated along a rift zone, where tectonic plates are pulling apart. As the crust thins and fractures, magma rises to fill the gap, creating volcanic activity. Rift volcanism typically produces more fluid lava flows rather than explosive blasts, which means communities near Hell's Half Acre in United States generally face slower-moving hazards like lava flows and ground fissures rather than sudden pyroclastic events. However, rift volcanoes can still generate significant ash emissions and gas releases that affect local air quality. The dominant rock type is basalt / picro-basalt, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Hell's Half Acre has 1 recorded eruption in the geological database, spanning from 3250 BCE to 3250 BCE.

GVP Reference Summary

Hell's Half Acre, the easternmost of the young basaltic lava fields of the Snake River Plain, covers an area of about 400 km2 SW of Idaho Falls. Basaltic lavas forming the broad, low shield volcano are dominantly pahoehoe flows that were erupted from a 3-km-long, NW-SE trending vent system at the NW part of the field during a brief eruptive episode about 5,200 years ago. The summit vent area contains an irregular, elongate 300 x 800 m central depression where a former lava lake fed late-stage flows. About 10 circular pit craters truncate the surface of the lava lake, and two prominent lava tube systems are located near the summit vent complex. Two major lava flow lobes, each about 5 km wide and 10 km long, extend to the S and SW along the flood plain of the Snake River and surround Morgans Pasture, a large kipuka. Interstate Highway 15 crosses the SE margin of the lava field SW of the city of Idaho Falls.

— Smithsonian Institution, Global Volcanism Program