America's Volcanic Past
|"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994|
|[NOTE: This list is just a sample of various Hawaii features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of Hawaii.]|
Excerpts from: Wood and Kienle, 1990, Volcanoes of North America: Cambridge University Press, contribution by Charles A. Wood; and USGS Hawaii Volcano Observatory Website, 2001
|Hawaiian "Hot Spot"|
Hawaiian "Hot Spot":2
Over the past 70 million years, the combined processes of magma formation, volcano eruption and growth, and continued movement of the Pacific Plate over the stationary Hawaiian "hot-spot" have left a long trail of volcanoes across the Pacific Ocean floor. The Hawaiian Ridge-Emperor Seamounts chain extends some 6,000 kilometers from the "Big Island" of Hawaii to the Aleutian Trench off Alaska. The Hawaiian Islands themselves are a very small part of the chain and are the youngest islands in the immense, mostly submarine mountain chain composed of more than 80 volcanoes. The length of the Hawaiian Ridge segment alone, from the Big Island northwest to Midway Island, is about equal to the distance from Washington, D.C. to Denver, Colorado (2,600 kilometers). The amount of lava erupted to form the Hawaiian-Emperor chain is calculated to be at least 750,000 cubic kilometers-more than enough to blanket the entire State of California with a layer of lava roughly 1.5 kilometers thick.
|Diamond Head State Monument|
Hawai'i's most famous landmark -- a large tuff cone which was formed by a short series of explosive eruptions some 100,000 years ago; National Natural Landmark. Picnicking on the crater floor in a landscaped meadow; detachment from the city. Moderate family hike (bring a flashlight) with panoramic view of Honolulu; trail 0.7 mile one-way and with some hazards. Viewpoint of Kahala plain. Park gate open 6 a.m. to 6 p.m.
How the Crater was Formed:8
The pronounced seaward summit, deeply eroded ridges, and ovoid-shaped crater are evidence of Le'ahi's (Diamond Head) very dynamic geological history. The creation of O'ahu began around 2.5 to 3 million years ago with volcanic eruptions from 2 shield volcanoes. A period of extensive erosion followed, leaving the Ko'olau and Wai'anae Mountain Ranges as the remnants of these very eroded volcanoes. After about 2 million years of volcanic inactivity, the southeastern end of the Ko'olau Range erupted. These eruptions occurred near the ocean where the magma was broken down into ash and fine particles by the water and steam. Blown into the air, these particles were cemented together into a rock called tuff which created tuff cones, such as Le'ahi. Le'ahi is believed to have been created about 300,000 years ago during a single, brief eruption. The broad, saucer-shaped crater covers 350 acres with its width being greater than its height. The southwestern rim is highest because winds were blowing ash in this direction during the eruption. Since the eruption, the slopes of the crater have been eroded and weathered by rain, wind, and the pounding of the sea. A coral reef now protects the seaward slopes of the crater. Today, Le'ahi is the most recognized landmark in Hawai'i. It was designated a National Natural Landmark in 1968 as an excellent example of a tuff cone.
|Haleakala National Park|
Haleakala is the easternmost of two shield volcanoes forming the island of Maui (more than 830,000 years ago), and is the third largest of all Hawaiian shield volcanoes, having a total volume of approximately 29,300 cubic kilometers.
Haleakala Crater is now a cool, cone-studded reminder of a once-active volcano. Streaks of red, yellow, gray, and black trace the courses of recent and ancient lava, ash, and cinder flows. The volcanic rocks slowly break down as natural forces reduce them to minute particles which are swept away by wind, heavy rain, and intermittent streams. The only known historical eruption at Haleakala (1790 A.D. +/- 3 years) occurred near La Perouse Bay and was witnessed by Hawaiians.
Lava Flows and Cinder Cones:4
Lava Flows and cinder cones (up to 180 meters high) completely cover the floor of Haleakala Crater.
|Hawaii Volcanoes National Park|
Hawaii Volcanoes National Park:6
Today Hawaii Volcanoes National Park displays the results of 70 million years of volcanism, migration, and evolution - processes that thrust a bare land from the sea and clothed it with complex and unique ecosystems and a distinct human culture. Created to preserve the natural setting of Kilauea and Mauna Loa, the park is also a refuge for islands native plants and animals and a link to its human past.
Kilauea, Mauna Ulu, and Pu'u O'o:7
Written records of Kilauea's activity began with arrival of Christian missionaries in 1823. The following century saw nearly continuous eruption in the caldera, punctuated by lava-lake subsidence and eruptions along both rift zones. Continuous summit activity ended in 1924 with deep subsidence and an explosive eruption at Halemaumau. Eruptions occurred intermittently in Halemaumau through 1934 and, following a hiatus, resumed in 1952. Eruptions returned to the east rift zone in 1955, and were frequent on both summit and flank until 1968; but in 1969 summit eruptions became less frequent as sustained activity began along the east rift zone. That activity so far has built lava shields and extensive flow fields and pyroclastic deposits at Mauna Ulu (1969-1974) and Pu'u O'o (beginning in 1983).
When Kilauea began to form is not known, but various estimates are 300,000-600,000 years ago. The volcano has been active ever since, with no prolonged periods of quiescence known. Geologic studies of surface exposures, and examination of drillhole samples, show that Kilauea is made mostly of lava flows, locally interbedded with deposits of explosive eruptions. Probably what we have seen happen in the past 200 years is a good guide to what has happened ever since Kilauea emerged from the sea as an island perhaps 50,000-100,000 years ago.
Kilauea and Halemaumau:7
Kilauea lies at the southeast end of the Hawaiian chain. It is the youngest major shield now protruding above sea level, but much of its bulk is under water. The subaerial part of Kilauea covers approximately 1,500 square kilometers. Its modern caldera contains an annulus of arcuate blocks stepped downward toward an inner sink, which is partly filled by a lava shield indented by Halemaumau crater. The modern caldera is thought to be nested within the buried rim of an older caldera. Two rift zones radiate from the summit. Kilauea probably began to grow about 200,000 years ago, and the oldest flows of Hilina Basalt now exposed in the fault scarps of the subaerial south flank probably date from 50-100 thousand years ago.
Mauna Loa and Mokua'aweoweo:7
Mauna Loa is considered the world's largest active volcano, with an estimated volume of more than 40,000 cubic kilometers, based on the assumption that the volcano extends from the surface to the top of the isostatically depressed ocean crust. However, because of adjacent volcanoes interfingering with Mauna Loa, and because older volcanic edifices may be buried at depth, the volcano's actual volume is probably less. The Mauna Loa shield is composed entirely of relatively thin flows of aa and pahoehoe, averaging 3 to 4 meters in thickness. Individual flows are typically less than one kilometer wide, but some are greater than 50 kilometers long. Mauna Loa's summit is indented by a 3 x 5-kilometer caldera up to 180 meters deep -- Mokua'aweoweo. ... Mauna Loa's summit -- elevation of 4,619 meters above sea level, and approximately 9 kilometers above the seafloor) -- is usually snow-covered in winter months.
1) Wood, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: Cambridge University Press
2) Kious and Tilling, This Dynamic Earth: The Story of Plate Tectonics: USGS Online Publication and
3) USGS Hawaii Volcano Observatory Website, January 2001
4) West, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: Cambridge University Press
5) U. S. National Park Service Website, Haleakala National Park, 2000
6) U. S. National Park Service Website, Hawaii Volcanoes National Park, Hawaii, 2000
7) Wood, Lockwood, and Holcomb, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: Cambridge University Press
8) State of Hawaii, Department of Land and Natural Resources Website, 2002
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