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Alignment of volcanic vents in the Hell's Half Acre - Lava Ridge volcanic rift zone

Dike Intrusion

Within the Snake River Plain, basalt eruptions result from dike intrusion. Dike intrusion is a process where magma within a tabular-shaped body ascends upward into or moves laterally within the earth’s upper crust. Distinct deformational landforms result from dike intrusion, including aligned basaltic vents, fissures, and, in some cases, sets of tension cracks, monoclines, and small normal faults that form small grabens. Where magmatic dikes intersect the surface, they erupt to form spatter cones, eruptive fissures, low shield volcanoes, and lava flows.

Basaltic vents and volcanic landforms are not randomly distributed within the Snake River Plain, but are concentrated in linear belts known as volcanic rift zones. Other active volcanic rift zones in Hawaii, USA and Krafla, Iceland have similar volcanic features. Volcanic rift zones trend northwest-southeast and extend 35 to 80 km (21.7 to 49.7 miles) from the northwest margin to the central and southeastern regions of the Snake River Plain. In contrast, the axial volcanic zone trends northeast-southwest along the axis of the Snake River Plain and has a high concentration of volcanic vents. Four volcanic rift zones and the axial volcanic zone cross INL.

The volcanic rift zones have features and lava flows that indicate they have been active through several cycles of volcanism. The ages of basalt flows within volcanic rift zones have been used to calculate recurrence intervals (or repeat times) of volcanism. The volcanic recurrence intervals are greater than 16,000 years for volcanic zones near INL.

Volcanic Zone

Recurrence Interval (years)

Arco

17,000

Axial

16,000

Great Rift

2,000

Howe-East Butte

100,000

Lava Ridge – Hell’s Half Acre

40,000

Several volcanic hazards associated with basaltic volcanism have been evaluated for INL facilities. The most significant hazards are ground deformation due to development of volcanic landforms, inundation of facilities by lava flows, and volcanic earthquakes. Other hazards are tephra fall and base surge.

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