Hawaiian Islands
 |
Map of the Hawaiian Islands, a chain of islands that stretches 2,400 km in a northwesterly direction from the southern tip of the Island of Hawai‘i. |
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. Politically, they form the U.S. State of
Hawaii.
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).
 |
Photograph of the Hawaiian Islands from Space Shuttle Discovery, looking southeast by south. Kaua‘i is closest at bottom right |
A total of 132 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:
*
Hawai‘i (also known as the Big Island)
*
Maui*
Kaho‘olawe (uninhabited; temporary residential facilities)
*
Lāna‘i*
Moloka‘i*
O‘ahu*
Kaua‘i*
Ni‘ihauSmaller islands, atolls, and reefs (beyond
Ni‘ihau and all uninhabited); called the
Northwestern Hawaiian Islands:
*
Ka‘ula*
Nihoa*
Necker (Mokumanamana)
*
French Frigate Shoals (Mokupāpapa)
*
Gardner Pinnacles (Pūhāhonu)
*
Maro Reef (Nalukakala)
*
Laysan (Kauō)
*
Lisianski Island (Papa‘āpoho)
*
Pearl and Hermes Reef (Holoikauaua)
*
Midway (Pihemanu) (temporary residential facilities)
*
Kure (Kānemiloha‘i)
Islets
 |
3-D perspective view of the southeastern Hawaiian Islands shown in green, with the white summits of Mauna Loa (4,170 m high) and Mauna Kea (4,206 m high). The islands are the tops of massive volcanoes, most of whose bulks lie below the sea surface. Ocean depths are colored from purple (5,750 m deep northeast of Maui) and blue to light gray (shallowest). Historical lava flows are shown in red, erupting from the summits and rift zones of Mauna Loa, Kilauea, and Hualalai volcanoes on Hawai‘i . |
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:
*
Ford Island (Moku‘ume‘ume)
*
Kaohikaipu *
Manana*
Mōkōlea Rock*
Nā Mokulua*
MolokiniExcept 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.
The chain of islands or
archipelago formed as the Pacific plate moves 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 (have been eroding far longer). The only active volcanism in the last 200 years has been on the southeastern island,
Hawaii, 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 Hawai‘i 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.
|
Eruptions from the Hawaii hotspot have left a trail of underwater mountains across the pacific over millions of years, called the Emperor Seamounts |
Hawai‘i (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 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 riversRelated 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
monocultural 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]
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.
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.
|
The top image above shows the winds around the Hawaiian Islands measured by the Seawinds instrument aboard QuikSCAT during August 1999. Trade winds blow from right to left in the image. The bottom image shows the ocean current formed by the islands' wake. Arrows indicate current direction and speed, while white contours show ocean temperatures. The warm water of the current generates winds which sustain the current for thousands of miles. |
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 Hawaii 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 Hawaii.
In addition, the wind wake drives an eastward "counter current" that brings warm water 8,000 kilometers from the Asian coast to Hawaii. 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.
 |
Aftermath of the 1960 Chilean tsunami in Hilo, Hawaii, where the tsunami left 61 people dead and 282 seriously injured. |
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.
*
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 Hawai‘i.
*
Introduction to Hawaiian Volcanism
