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Not every volcano is a mountain. Fissure volcanoes erupt along elongated cracks instead of a single central vent, and they have produced the largest-volume eruptions in Earth's history in terms of lava erupted. This page follows the National Park Service's volcano series.
The Kings Bowl lava field, Craters of the Moon National Monument and Preserve, erupted from a fissure. NPS photo by Douglas Owen.
How they work
A fissure eruption happens when a magma-filled dike, a tabular igneous intrusion, reaches the surface. The vents are elongated, usually parallel to rifts and other fracture systems. Fissure eruptions seldom build substantial edifices. Instead they feed lava flows that can travel great distances, and how far depends on magma supply, viscosity (runnier lava goes farther) and eruption rate. Apart from low spatter cones built where still-molten bombs pile up around fire-fountains, there are no hills. Size depends on the magma supply and the fissure's length.
- Lava: mostly basalt to basaltic andesite, though lava of any composition can erupt from a fissure.
- Style: mostly nonexplosive (effusive), usually 0 on the Volcanic Explosivity Index and up to 1. Basaltic eruptions are typically Hawaiian in style, with lava flows and sometimes fire-fountains. Very large ones can have profound environmental consequences because of the volume of gas erupted with the lava.
- Where: in oceanic and continental settings, often in extensional areas and monogenetic volcanic fields, and on the flanks of shield volcanoes.
Fissure volcanoes in national parks
At least four National Park System units contain fissure volcanoes.
| Park | What is there |
|---|---|
| Craters of the Moon National Monument and Preserve, Idaho | Three lava fields (Craters of the Moon, Wapi and Kings Bowl) lined up along the Great Rift on the Snake River Plain. Fissures fed the basaltic flows, and cinder cones and spatter cones line up along them. The Trench Mortar Flat flow erupted from fissures about 2,100 years ago. |
| El Malpais National Monument, New Mexico | Twin Craters, small cinder cones along a fissure, fed a flow about 18,000 years ago. The park holds part of the Zuni-Bandera Volcanic Field. |
| Lava Beds National Monument, California | Lava flows from fissures on the flank of Medicine Lake Volcano, a large shield mostly outside the monument. The Ross Chimneys flow erupted from numerous vents along a 1.6-mile (2.5 km) fissure about 3,140 years ago. |
| Petroglyph National Monument, New Mexico | Five small volcanic cones along a fissure that erupted about 156,000 years ago, on the west side of Albuquerque in the Rio Grande Rift. |
Vents aligned along an eruptive fissure at Craters of the Moon. NPS photo.
Ross Chimneys spatter vents, Lava Beds National Monument, with Medicine Lake Volcano on the horizon. USGS photo.
Three small spatter cones along a fissure in Petroglyph National Monument. NPS photograph by Chanteil Walter.
On shield volcanoes
Kīlauea and Mauna Loa, the big shield volcanoes at Hawai'i Volcanoes National Park, have active rift zones, areas of weakness where magma travels in dikes and erupts on the flanks away from the summit. A 2018 fissure eruption on Kīlauea's Lower East Rift Zone sent lava fountains up to 150 feet (45 m) and built a spatter cone.
The 2018 Lower East Rift Zone eruption. USGS photo.
The Columbia River Basalts
The Columbia River Basalt Group came from the largest eruptions in North America's history. They are flood basalts: thick piles of lava flows erupted in a short time over a vast area. They cover more than 81,000 square miles (210,000 square km), with an estimated volume of 50,000 cubic miles (210,000 cubic km), mostly erupted between 16.7 and 15.5 million years ago. The lava came from fissures, mostly in eastern Oregon, southeastern Washington and Idaho. Flows up to 13,000 feet (4,000 m) thick filled much of the Columbia Basin, and some reached the Oregon-Washington coast. The dike swarms that fed them run north-northwest, with fissures as long as 110 miles (180 km).
These basalts show up in several park sites in the Northwest, including Nez Perce National Historical Park, John Day Fossil Beds National Monument, Lake Roosevelt National Recreation Area and Manhattan Project National Historical Park.
Columbia River Basalts exposed in Joseph Canyon, Nez Perce National Historical Park. NPS photo.
What to look for
- Basaltic lava flows, fluid enough to travel far in pāhoehoe and 'a'ā forms, though fissures sometimes erupt blocky flows.
- Lava tubes, found in fissure-fed flows at Craters of the Moon, El Malpais and Lava Beds.
- Spatter cones, steep-sided low cones of fused-together volcanic bombs that landed molten, usually smaller than 33 feet (10 m), often in lines along fissures.
Hazards
A single fissure may erupt only once, but the fields and shield-volcano flanks that host them erupt repeatedly, and new fissure eruptions can open near old ones. Warning signs include earthquakes and underground rumblings. On and around fissure volcanoes, hazards include rough, uneven ground, fracture systems, crevasses and lava tube caves.
Sources
- National Park Service, Fissure Volcanoes, part of the volcano series; rewritten in hubnx's own words. The source's Petroglyph heading says California, but its own text puts the park in Albuquerque, New Mexico.
In these publicationsFort Vancouver National Historic SiteLava Beds National MonumentCraters Of The Moon National Monument & PreserveJohn Day Fossil Beds National MonumentHagerman Fossil Beds National MonumentEl Malpais National Monument
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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