Hawaiian Islands
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The Hawaiian Islands, once known as the Sandwich Islands, form an archipelago of nineteen islands and atolls, numerous smaller islets, and undersea seamounts trending northwest by southeast in the North Pacific Ocean between latitudes 19° N and 29° N. The archipelago takes its name from the largest island in the group and extends some 1500 miles (2400 km) from the Island of Hawaiʻi in the south to northernmost Kure Atoll. Excluding Midway, which is an unincorporated territory of the United States, the Hawaiian Islands form the U.S. State of Hawaiʻi.
This archipelago represents the exposed peaks of a great undersea mountain range known as the Hawaiian-Emperor seamount chain, formed by volcanic activity over a hotspot in the earth's mantle. At about 3,000 km (1,860 miles) from the nearest continent, the Hawaiian Island archipelago is the most isolated grouping of islands on Earth (Macdonald, Abbott, and Peterson, 1984).
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[edit] Islands and reefs of the Hawaiian archipelago
The Hawaiian Islands comprise a total of 137 islands and atolls, with a total land area of 16,636 km² (6,423.4 square miles).
The eight main Hawaiian islands (also known as the Hawaiian Windward Islands) are listed here from south to north. All except Kahoʻolawe are inhabited.
- Hawaiʻi (also known as the Big Island)
- Maui
- Kahoʻolawe (uninhabited; temporary residential facilities)
- Lānaʻi
- Molokaʻi
- Oʻahu
- Kauaʻi
- Niʻihau
Smaller islands, atolls, and reefs (beyond Niʻihau and all uninhabited); called the Northwestern Hawaiian Islands, or Hawaiian Leeward Islands:
- Nihoa (Mokumana)
- Necker (Mokumanamana)
- French Frigate Shoals (Mokupāpapa)
- Gardner Pinnacles (Pūhāhonu)
- Maro Reef (Nalukakala)
- Laysan (Kauō)
- Lisianski Island (Papaʻāpoho)
- Pearl and Hermes Atoll (Holoikauaua)
- Midway Atoll (Pihemanu) (temporary residential facilities)
- Kure Atoll (Kānemilohaʻi)
[edit] Islets
Some information sources state that there are 137 "islands" in the Hawaiian chain. This number includes all minor islands and islets offshore of the main islands (listed above) and individual islets in each atoll. (Hawaiʻi state government, undated). Following is a list of islets and small offshore islands that make up the total count beyond 19:
- Ford Island (Mokuʻumeʻume)
- Lehua
- Kaʻula
- Kaohikaipu
- Manana
- Mōkōlea Rock
- Nā Mokulua
- Molokini
- Mokoliʻi
- Moku Manu
Except for Midway, which is an unincorporated territory of the United States, these islands and islets are administered as the State of Hawaii — the 50th state of the United States of America.
[edit] Geology
The chain of islands or archipelago formed as the Pacific plate moved slowly northwestward over a hotspot in the Earth's mantle at about 52 km (32 miles) per million years. Hence the islands in the northwest of the archipelago are older and typically smaller, due to longer exposure to erosion. The only active volcanism in the last 200 years has been on the southeastern island, Hawaiʻi, and on the submerged but growing volcano at the extreme southeast, Loihi. The Hawaiian Volcano Observatory of the U. S. Geological Survey documents recent volcanic activity and provides images and interpretations of the volcanism.
Almost all magma created in the hotspot has the composition of basalt, and so the Hawaiian volcanoes are constructed almost entirely of this igneous rock and its coarse-grained equivalents, gabbro and diabase. A few igneous rock types with compositions unlike basalt, such as nephelinite, do occur on these islands but are extremely rare. The majority of eruptions in Hawaiʻi are Hawaiian-type eruptions because basaltic magma is relatively fluid compared with magmas typically involved in more explosive eruptions, such as the andesitic magmas that produce some of the spectacular and dangerous eruptions around the margins of the Pacific basin.
Hawaiʻi (the Big Island) is the largest and youngest island in the chain, built from five different volcanoes. Mauna Loa, comprising over half of the Big Island, is the largest shield volcano on the planet. The measurement from sea level to summit is more than 4km, from sea level to sea floor about 5km. (USGS)
See also: List of Hawaiʻi rivers
[edit] Earthquakes
The Hawaiian Islands are the site of many earthquakes. Generally, they are caused by the islands' volcanic foundations. Most of the early earthquake monitoring took place in Hilo, by Sarah J. Lyman and her family. From 1833 to 1896, approximately 4 or 5 earthquakes were reported per year.[1]
The state of Hawaii accounted for 7.3% of the United States' reported earthquakes with a magnitude 3.5 or greater from 1974 to 2003, with a total 1533 earthquakes. Hawaii ranked as the state with the third most earthquakes over this time period.[2]
On Sunday, October 15, 2006, there was an earthquake with a magnitude of 6.7, off the northwest coast of the island of Hawaii, near the Kona area of the big island. The initial earthquake was followed approximately five minutes later by a magnitude 5.7 aftershock. Minor-to-moderate damage was reported on most of the big island, including several major roadways rendered impassable by rock slides, and other structural damage, and effects were felt as far away as Honolulu, Oahu, nearly 150 miles from the epicenter. Power outages lasted for several hours on several islands and several water mains ruptured.
Linda Lingle, the governor of Hawaii made a statewide disaster declaration several hours after the earthquake struck. A tsunami alert was issued, but quickly canceled after sensor buoys failed to detect significant wave activity. No deaths or life-threatening injuries were reported.
Most of the earthquakes are reported by the Hawaiian Volcano Observatory established by the USGS.
[edit] Ecology
- Related article: Endemism in the Hawaiian Islands.
The Hawaiian Islands are home to a large number of endemic species. The plant and animal life of the Hawaiian Islands developed in nearly complete isolation over about 70 million years. Mammals were absent until they arrived with the first human settlers.
Human contact, first by Polynesians, introduced new trees, plants and animals. These included voracious species such as rats and pigs, who took a heavy toll on native birds and invertebrates that evolved in the absence of such predators. The growing population also brought deforestation, forest degradation, treeless grasslands, and environmental degradation. As a result, many species which depended on forest habitats and food went extinct. As humans cleared land for farming, monocultural crop production replaced multi-species systems.
The arrival of the Europeans had a significant impact, with the promotion of large-scale single-species export agriculture and livestock grazing. In turn, this led to the increased clearing of forests, and the development of towns, driving more species to extinction. Today, many of the remaining endemic species are considered endangered. [1]
[edit] Climate
The islands receive most rainfall from the trade winds on their north and east flanks (called the windward side) as a result of orographic precipitation. Coastal areas in general and especially the south and west flanks or leeward sides, tend to be drier. Because of the frequent build-up of Tradewind clouds and potential showers, most tourist areas have been built on the leeward coasts of the islands.
In general, the Hawaiian Islands receive most of their precipitation during the winter months (October to April). Drier conditions generally prevail from May to September, but the warmer temperatures increase the risk of hurricanes (see below).
Temperatures at sea level generally range from high temperatures of 85-90°F (29-32°C) during the summer months to low temperatures of 65-70°F (18-21°C) during the winter months. Very rarely does the temperature rise above 90°F (32°C) or drop below 60°F (16°C) at lower elevations. Temperatures are lower at higher altitudes; in fact, the three highest mountains of Mauna Kea, Mauna Loa, and Haleakala sometimes receive snowfall during the winter.
[edit] Hurricanes
The hurricane season in the Hawaiian Islands is roughly from June through November, when hurricanes and tropical storms are most probable in the North Pacific. These storms tend to originate off the coast of Mexico (particularly the Baja California peninsula) and track west or northwest towards the islands.
Hawai‘i is protected by the vastness of the Pacific (i.e. the improbability of a direct hit); as storms cross the Pacific they tend to lose strength if they bear northward and encounter cooler water. It is thought that the topography of the highest islands (Haleakalā on Maui, Mauna Kea and Mauna Loa on the Big Island) may protect these islands, and certainly Kauaʻi has been hit more often in the last 50 years than the others.
[edit] Effect on trade winds
Despite being a tiny speck of land within the vast Pacific Ocean, the Hawaiian Islands have a surprising effect on ocean currents and circulation patterns over much of the Pacific. In the Northern Hemisphere, the trade winds blow from northeast to southwest, from North and South America toward Asia, between the equator and 30 degrees north latitude. Typically, the trade winds continue on an uninterrupted course across the Pacific — unless something gets in their way, like an island.
Hawaii's high mountain landscape presents a substantial obstacle in the path of the trade winds. The elevated topography blocks the airflow, effectively splitting the trade winds in two. This split causes a zone of weak winds, called a "wind wake," to form on the leeward side of the islands.
Aerodynamic theory indicates that an island wind wake effect should dissipate within a few hundred kilometers and not be felt in the western Pacific. However, the wind wake caused by the Hawaiian Islands extends 3,000 kilometers, which is roughly 10 times longer than any wake observed elsewhere. The long wake testifies to the strong interaction between the atmosphere and ocean, which has strong implications for global climate research. It helps researchers assess climate sensitivity, namely how much increase can be observed in the global mean temperature as carbon dioxide levels increase. It is also important for understanding natural climate variations, like El Niño.
There are number of reasons why this phenomenon has only been observed in Hawaii. First, because the ocean reacts slowly to fast-changing winds, the wind system must be steady to exert forcing on the ocean, as is the case with the trade winds. Second, the high mountain topography of Hawaiʻi provides a significant disturbance to the winds. Third, the Hawaiian Islands are large in horizontal scale, extending over four degrees in latitude. It is this active interaction between wind, ocean current, and temperature that creates this uniquely long wake west of Hawaiʻi.
In addition, the wind wake drives an eastward "counter current" that brings warm water 8,000 kilometers from the Asian coast to Hawaiʻi. This warm water drives further changes in wind, allowing the island effect to extend far into the western Pacific. The counter current had been observed by oceanographers near the Hawaiian Islands years before the long wake was discovered, but they did not know what caused it.[3]
[edit] Tsunamis
The Hawaiian Islands can be affected by tsunamis, great waves that strike the shore typically but not exclusively from the north. Tsunamis are movements of the surface layer of the ocean most often caused by earthquakes somewhere in the Pacific. The city of Hilo on the Big Island has historically been most impacted by tsunamis, where the inrushing water is accentuated by the shape of the bay on which the town is situated.
[edit] See also
- Hawaii
- Hawaiian people
- Hawaiian language
- History of Hawaii
- Kingdom of Hawaii
- Hawaiian sovereignty movement
- Ancient Hawaii
- Hawaiian mythology
[edit] References
- ^ http://earthquake.usgs.gov/regional/states/hawaii/history.php
- ^ http://earthquake.usgs.gov/regional/states/top_states.php
- ^ Schmidt, Laurie J. (October 2, 2003). Little Islands, Big Wake. NASA Earth Observatory. Retrieved on May 16, 2006.
- Hawai‘i state government, Table 05.09 (.pdf file).
- An integrated information website focused on the Hawaiian Archipelago from the Pacific Region Integrated Data Enterprise (PRIDE).
- Macdonald, G. A., A. T. Abbott, and F. L. Peterson. 1984. Volcanoes in the Sea. The Geology of Hawaii, 2nd edition. University of Hawaii Press, Honolulu. 517 pp.
- The Ocean Atlas of Hawai‘i - SOEST at University of Hawaiʻi.
- Introduction to Hawaiian Volcanism
