Cleft Segment

Geography & Climate

Cleft Segment is located in Undersea Features, within the Northeast Pacific Rifts Volcanic Province of the broader Eastern Pacific Volcanic Regions. Situated at 44.83° N, 130.30° W in the Northern Hemisphere, the volcano lies within a temperate climate zone. With an elevation of -2,140 meters — below sea level — Cleft Segment is a submarine or submerged volcanic feature. Submarine volcanoes make up the majority of Earth's volcanic activity, though most eruptions go unobserved beneath the ocean surface. The volcanic landform is characterized as a cluster, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Cleft Segment 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 Cleft Segment in Undersea Features 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

Cleft Segment has 3 recorded eruptions in the geological database, spanning from 270 BCE to 1986 CE. These eruptions span roughly 2,256 years of volcanic history. The most recent eruption in 1986 CE places this volcano within the modern era of volcanological observation.

GVP Reference Summary

The Cleft Segment, the southernmost of the Juan de Fuca Ridge, lies immediately north of the Blanco Fracture Zone. The 80-km-long segment is named for a nearly continuous 10-km-long, 30-50 m wide cleft at its southern end. Two episodes of seafloor spreading were documented along the northern part of the segment in the 1980's. Bathymetric surveys indicated that a series of discontinuous pillow-lava mounds were extruded along a 17-km-long fissure between 1981 and 1987. The eruption possibly coincided with emission of a large plume of hot mineral-laden water in 1986. The location is at a depth of about 2,300 m near the northern edge of the Cleft segment and the southern end of the Vance segment of the Juan de Fuca Ridge, about 500 km W of the central Oregon coast. Youthful sheet-lava flows immediately south of the pillow lavas were estimated to be only a few years older.

— Smithsonian Institution, Global Volcanism Program