Kohala (mountain)

Infobox Mountain
Name=Kohala Mountains
Photo=Kohala volcano.jpeg
Caption=A view of Kohala Volcano from the slopes of Mauna Kea
Elevation=convert|5480|ft|m|0cite web
title = Kohala - Hawai`i's Oldest Volcano
work = Hawaiian Volcano Observatory
publisher = United States Geological Survey
date = 1998-03-20
url = http://hvo.wr.usgs.gov/volcanoes/kohala/
format = HTML
accessdate = 2008-08-22]
Coordinates=coord|20|05|10|N|155|43|02|W|type:mountain_region:USFact|date=August 2008
Location=Hawaii, USA
Topographic
USGS Kamuela
Range=Hawaiian Islands
Type=Shield volcano
Volcanic_Arc/Belt=Hawaiian-Emperor seamount chain
Age=460,000-120,000 yr

Kohala, also known as the "Kohala ," is the name of an extinct volcano on Hawaii Island in the state of Hawaii. At its highest elevation, Kohala is convert|5480|ft|m|0 above sea level.

Kohala is believed to be the oldest volcano that makes up Hawaii Island, which was formed by the Hawaii hotspot. It is thought to have breached sea level about 500,000 years ago. Its eruptive activity began to wane about 300,000 years ago. At about this time, it is thought that the volcano was about twice as wide as it is today. However, because the island of Hawaii is slowly sinking into the Pacific Ocean's seafloor, the volcano began to sink faster than new eruptions could replace what was being lost to subsidence. Thus, the volcano's size began to recede as it sank below sea level. Kohala's activity continued to wane and it is thought that the volcano last erupted about 120,000 years ago, with potassium-argon dating indicating the last eruptions were in the late Pleistocene. [cite journal | last = McDougall | first = Ian | title = Potassium-argon ages on lavas of Kohala volcano, Hawaii | journal = GSA Bulletin | volume = 80 | issue = 12 | pages = pp. 2597–2600 | publisher = Geological Society of America | location = | date = December 1969 | url = | doi = | accessdate = ]

The Island of Hawaiokinai is built from five separate shield volcanoes that erupted somewhat sequentially, one overlapping the other. These are (from oldest to youngest):
*Kohala (extinct)
*Mauna Kea (dormant)
*Hualālai (dormant)
*Mauna Loa (active, partly within Hawaiokinai Volcanoes National Park)
*Kīlauea (very active; part of Hawaiokinai Volcanoes National Park)

As Kohala slowly waned, its southern flanks were buried by the two younger volcanoes, Mauna Kea and Mauna Loa. Since Kohala'a southern flanks are buried, it is difficult to determine the size and shape of the volcano when it was at its prime.

About 110,000 years ago, a large landslide on the northeastern flank of the volcano removed a massive portion of the mountain, [cite journal | last = McMurtry | first = Gary M. | coauthors = Gerard J. Fryer, David R. Tappin, Ian P. Wilkinson, Mark Williams, Jan Fietzke, Dieter Garbe-Schoenberg and Philip Watts | title = Megatsunami deposits on Kohala volcano, Hawaii, from flank collapse of Mauna Loa | journal = Geology | volume = 32 | issue = 9 | pages = pp. 741–744 | publisher = Geological Society of America | location = | date = September 2004 | url = | doi = 10.1130/G20642.1 | accessdate = ] estimated to be as much as a section convert|20|km|mi|0|sp=us 20 kilometers wide. The part of the mountain removed by the landslide collapsed into the ocean at a very high speed and traveled as much as convert|130|km|mi|0|sp=us 130 kilometers across the ocean floor. The large seacliffs on the northeast flank of the volcano mark the headwall of this landslide.

References