Statewide County HI Archives News.....Wiki Mo'olelo Part 11 . November 5, 2008 ************************************************ Copyright. All rights reserved. http://www.usgwarchives.net/copyright.htm http://www.usgwarchives.net/hi/hifiles.htm ************************************************ File contributed for use in USGenWeb Archives by: Darlene E. Kelley donkeyskid@msn.com November 16, 2008, 8:51 am Keepers Of The Culture, A Study In Time Of The Hawaiian Islands November 5, 2008 Contributed for use in USGenWeb Archives by Darlene E. Kelley donkeyskid@msn.com. November 5, 2008 +++++++++++++++++++++++++++++++ Historical Collections of Hawai'i Keepers of the Culture A Study in Time, of the Hawai'ian Islands Wiki Mo'olelo - part 11 by Darlene E. Kelley +++++++++++++++++++++++++++++++ Wiki Mo'olelo Part 11. Hawai'ian Islands - Volcanic in Origin. The Hawai'ian Islands are volcanic in origin with each island made up of a least one primary volcano, although many islands are composites of more than one. The Big Island, for instance is constructed of 5 major volcanos; Kilauea, Mauna Loa, Mauna Kea, Hualalai, and Kohala. Mana Loa is the largest active volcano on Earth ( in terms of how much lava it erupts each year). The primary volcanoes, mentioned above, on each island are known as shield volcanoes, which are gently sloping mountains produced from a large number of generally very fliud lava flows. Hawai'ian volcanoes primarily erupt a tpe of rock known as basalt. When molten, basalt produces liquids of relatively high fluidity, compared to volcanoes that erupt more silica rich magma types such as andesite, dacite, or rhyolite. The fluidity of molten basalt favors the formation of lava flows, which is why the Hawaiian volcanoes generally have gentle sloing sides. By contrast, lavas with higher silica content are more viscous and commonly produce either thicker, shorter lava flows, thick blocky deposits and /or thick beds of ash that fall from the sky following explosive eruptions. These other types of volcanoes ( common outside of Hawai'i ) are typically steeper sided. Each of the Hawai'ian islands formed over a " hotspot " ( about 21 degress north of the Eqauator ). A hotspot is the result of a persistent region of molten or melted rock known as magma. There are at least 50 hotspots world wide and they occur at several places beneath the moving plates of the earth's crust. The earth's crust is divided into a dozen or so moving plates, called tectonic plates. The plate that is over the Hawai'ian hotspot is called the Pacific Plate. These tectonic plates are adrift on the molten magma beneath. The Pacific Plate is currently moving northwest about 3 -1/2 inches per year. Thus when a volcano forms over the Hawai'ian hotspot, it is eventually pulled northwest and becomes extinct. ( i.e. Hawai'ian Islands). In this way, a chain of volcanoes is produced. Melted rock or magma generated from the hotspot rises buoyantly because it is lighter than the surrounding rocks Earthquake patterns suggest that the magma rises up through cracks in the tectonic plate, piercing the earth's crust and erupting onto the seabed floor. When a submarine volcano grows tall enough to rise above the ocean's surface it becomes an island. This how all of the Hawai'ian islands were formed. The Big Island ( Mauna Loa ) rises up 32.000 feet frm the ocean floor ( making it the largest mountain on earth ), though only the top 13,800 feet are above sea level. Hawai'i is in the center of the Pacific Plate, surrounded on all sides by subduction volcanoes. These occur when one plate " subducts " beneath another creating tremendous pressure which is released via vocano vent. Vocanoes all around the edges of the Pacific plate form what is known as the Pacific Ring of Fire. These Pacific Rim volcaoes include Japan, New Zealand, Alaska, and the Pacific Northwest. But Hawaiian vocanos are unique. +++++++++++++++ Hawai'ian Shield Volcanoes The main Hawai'ian Islands are the tops of giant undersea shield volcanoes that formed at the Hawai'ian hotspot. which is presntly under the Big Island of Hawai'i. Shield volcanoes are genty sloping mountains produced from a large number of generally very fluid lava flows. There are 8 main islands, which make up the State of Hawai'i. They are; Hawaii, Maui, Oahu, Kahoolawe, Lanai, Molokai, Kauai and Niihau. There is one additional small island near Niihau that is often overlooked and that is Kaala. The outer Hawai'ian Ilsands ( aka the Northwest Hawai'ian Islands ) are a series of 9 older land masses north of Kauai that extend from Nihoa to Kure and which ar the above sea level remnants of once much larger volcanic mountains. Together these make 18 commonly accepted islands. Depending on how one counts them, there are also more than a hundred additional small rocks and islets among the Hawai'ian Islands that are either volcanic, marine sedimentary or erosional in orgin, which when combines with the other 18, total to perhaps as many as 130 or so in the entire Archipelago. +++++++++++ Hawai'ian Volcano Age trends The aging of the islands with distance from the current hot spot is where distance along the chain is approximated as distance away from Kilauea volcano. the youngest above sea level. In fact, even beyond Kure the Hawai'ian chain continues as a series of now submerged former islands known collectively as the Emperior seamounts. The two primary volcanoes that make up O'ahu where Honoulu is, have not erupted for well over a million years. The increasing age of the Hawai'ian Archipelago is as follows from Northwest to southeast; Starting with Kure in the Northwest; Midway; Pearl & Hermes Reef; Fisher Reef/ Neva Shoal; Laysan; Maro Reef; Raita bank; Gardner; French Frigate Shoals; Necker; Nihoa; Niihau; Kaua'i; O'ahu; Moloka'i; Mau'i; Hawai'i; and Loiha. The age trend of the volcanoes is thought to be due to the way in which the islands are built on the moving sea floor of the North Pacific Ocean: the Pacific Ocean is mostly floored by a single tectonic plate. known as the Pacific Plate. and that it is moving over the layer in the Earth known as the Asthenosphere. This movement takes it to the nortwest compared to the layers below it at a rate of 5 to 10 cm/yr. As the plate moves over a fixed spot deeper in the earth where magna ( molten lava) forms, a new volcano can punch through this plate and creat an island. The Hawai'ian Islands ae believed to be formed from such hot spot. As the plate moves away, the volcano stops erupting and a new one is formed in its place. With time, the volcanoes keep drifting westward and getting older relative to the one active volcano that is over the hot spot. As they age,the crust upon which they sit, cools and sbusides. This, combined with erosion of the islands once active volcanism stops, leads to a shrinking of the islands with age and their eventual submergence below the ocean surface. Importantly, the time over which various active volanoes on the islands remain active is long ( hundreds of thousand years ) so that significeient overlap in ages occurr on neighboring islands. For instance; although Heleakala volcano on Mau'i is a great distance away from the presently erupting Kilauea, Haleakala last erupted only about 200 years ago. Currently there are 3 Hawai'ian volcanoes that we can classify as active; 1.-- Kilauea, actively erupting since 1983 2.-- Mauna Loa, which erupted in 1984 and is building for a new eruption soon. 3.--Loihi, which erupted in 1996. All three of these active Hawai'ian volcanoes share the Hawai'ian hot spot, but retain unique volcanic histories and composition. The most likely Dormant volcanos are; 1.- Hualalai, which erupted in 1801. 2.- Haleakala, which erupted in about 1790. a distance of 182 km of Kilauea. 3.- Mauna Kea, hich erupted about 4,000 years ago. a distance of 54 km from Kilauea. +++++++++++++++ O'ahu & volcanoes The island of O'ahu is formed from two principle volcanoes; Waianae and Koolau Waianae is about 2.2-3.8 million years old and Koolau is about 1,8-2.6 million years old. They are now dead volcanoes. The island is also riddled in spots by smaller volcanic features such as Diamond Head, Punchbowl, Salt Lake crater, Kolo head and Koko crater, etc. These smaller volcanos formed in more recent times, although age determinations on them are not very good. In general, these features ( sometimes called " post eriosional " or rejuvenation " volcanoes) are believed to be between 70,000 or 500,000 years old. Some believe that some flows in Honolulu are younger ( 5000 -10000 years old ) but the evidence is not very convincing. So, is there a threat of a volcano erupting there again, it is always possible, but the odds are very slim. One way volcanologists predict eruptive activity at locales that erupt very infrequently is to look at the historical frequency of eruptions in the area in the past. Although the data is limited, the suggestion is that post erosional series on O'ahu experienced eruptions every few tens of thousands of years.Since it as been longer than that since the last eruption, it may be that activity is now finally over. One other bit of info regarding volcanic hazards is that these small volcanoes usually erupt only once. A new eruption in the area would create a new small volcano, instead of occupying an older one. +++++++++++++++ Vocanoes of the Islands & age Island Volcano age ( million years) Hawaii Mauna Loa 0.1- 0.5 Kohala 0.06- 0.45 Maui Haleakala 0.41 - 0.86 West Maui 1.2 - 1.6 Kahoolawe Kahoolawe 1.0 Lanai Lanai 0.81 - 1.5 Molokai East Molokai 1.3 - 1.75 West Molokai 1.5 - 1.8 Oahu Post errosional 0.03 -1.3 Koolau 1.8 - 2.6 Waianae 2.2 - 3.8 Kauai Koloa 1.41 - 1.43 Makaweli 3.5 - 4.1 Napali 4. 4 - 5.7 Nihoa Nihoa 7.5 Necker Necker 11.3 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Next Part 12 File at: http://files.usgwarchives.net/hi/statewide/newspapers/wikimool93nnw.txt This file has been created by a form at http://www.genrecords.net/hifiles/ File size: 10.5 Kb