Hawaiian Islands

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Image:Hawaiianislandchain USGS.png 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 Hawai‘i in the south to northernmost Kure Atoll.

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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Islands and reefs of the Hawaiian archipelago

Image:Hawaii sts26 big.jpg

A total of 19 islands and atolls comprise the Hawaiian Islands, with a total land area of 16,636 km2 (6,423.4 square miles).

The eight main Hawaiian islands (all inhabited except for Kaho‘olawe) are, listed here from south to north:

Smaller islands, atolls, and reefs (beyond Ni‘ihau and all uninhabited); called the Northwestern Hawaiian Islands:

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Islets

Image:2003-3d-hawaiian-islands-usgs-i2809.jpg

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. (Hawai‘i state government, undated). Following is a list of islets and small offshore islands that make up the total count beyond 19:

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.

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Geology

The chain of islands or archipelago formed as the Pacific plate moves slowly northwestward over a hotspot in the earth's crust at about 52 km (32 miles) per million years. Hence the islands in the northwest of the archipelago are older and typically smaller (have been eroding far longer).

Because of the composition of the magma in the hotspot, the composition of Hawaiian volcanoes is basaltic. The majority of eruptions in Hawai‘i are Hawaiian-type eruptions because basaltic magma is relatively fluid compared with andesitic eruptions.

Image:Hawaii hotspot.jpg

Hawai‘i (the Big Island) is the largest and youngest island in the chain, built from seven different volcanoes. Mauna Loa, comprising over half of the Big Island, is the largest shield volcano on the planet. The measurement from the base locally depressing the sea floor in the Hawaiian Trough to its peak is about 17 km (56,000 feet; USGS)

See also: List of Hawaii rivers

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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.

Human contact, first by Polynesians, introduced new trees, plants and animals. 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. Agriculture began to increase, with monocultual crop production replacing 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]

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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.

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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 Kaua‘i has been hit more often in the last 50 years than the others.

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Tsunamis

Image:1960-Chilean-tsunami-Hilo-HI-USGS.jpg 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.

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References

et:Hawaii saared fr:Archipel d'Hawaii ja:ハワイ諸島 ko:하와이 제도 pl:Hawaje simple:Hawaiian Islands vi:Hawaii

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