Hawaii Islands

Hawaii’s Islands

Hawaii’s diverse natural scenery, warm tropical climate, abundance of public beaches, oceanic surroundings, and active volcanoes make it a popular destination for tourists, (wind) surfers, biologists, and volcanologists alike. Due to its mid-Pacific location, Hawaii has many North American and Asian influences along with its own vibrant native culture. Hawaii has over a million permanent residents along with many visitors and U.S. military personnel. Its capital is Honolulu on the island of Oʻahu.

The state encompasses nearly the entire volcanic Hawaiian Island chain, which comprises hundreds of islands spread over 1,500 miles (2,400 km). At the southeastern end of the archipelago, the eight "main islands" are (from the northwest to southeast) Niʻihau, Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Kahoʻolawe, Maui and the island of Hawaiʻi. The last is the largest and is often called "The Big Island" to avoid confusing the name of the island with the name of the state as a whole. The archipelago is physiographically and ethnologically part of the Polynesian subregion of Oceania.

Hawaii is the 8th smallest, the 11th least populous, but the 13th most densely populated of the 50 U.S. states. Hawaii's ocean coastline is approximately 750 miles (1,210 km) long, which is fourth in the United States after those of Alaska, Florida and California.

Hawaii is one of two states that do not observe daylight saving time, the other being Arizona. It is also one of two states that are not in the Contiguous United States; the other is Alaska, however, Hawaii is the only U.S. state not to be located in the Americas. Hawaii is also the only state with an Asian plurality.

Hawaii paradise

Geology

rigin of the Hawaiian Islands

The Hawaiian Islands are the tops of gigantic volcanic mountains formed by countless eruptions of fluid lava over several million years; some tower more than 30,000 feet above the seafloor. These volcanic peaks rising above the ocean surface represent only the tiny, visible part of an immense submarine ridge, the Hawaiian Ridge—Emperor Seamount Chain, composed of more than 80 large volcanoes.

This range stretches across the Pacific Ocean floor from the Hawaiian Islands to the Aleutian Trench. The length of the Hawaiian Ridge segment alone, between the Island of Hawai'i and Midway Island to the northwest, is about 1,600 miles, roughly the distance from Washington, D.C., to Denver, Colorado. The amount of lava erupted to form this huge ridge, about 186,000 cubic miles, is more than enough to cover the State of California with a layer 1 mile thick.

Map of the Pacific Basin showing the location of the Hawaiian Ridge-Emperor Seamount Chain and the Aleutian Trench. Base map from "This Dynamic Planet"

Hawaii is geologically a unique place on Earth because it is caused by a 'hot spot.' Most islands are found at tectonic plate boundaries either from spreading centers (like Iceland) or from subduction zones (like the Aleutian Islands). There are few 'hot spots' on Earth and the one under Hawaii is right in the middle of one of the largest crustal plates on Earth - the Pacific Plate. A geologic 'hot spot' is an area in the middle of a crustal plate where volcanism occurs. It is easy to geologically explain the volcanism at plate spreading centers and subduction zones but not as easy to explain a 'hot spot.' The molten magma breaks through the crustal plate (theories describe this as either from a weak/thin part of the plate or a particularly hot part of the molten magma). A hot spot under the American plate is why Yellowstone National Park has geysers and other thermal features. If the hot spot is under the seafloor (as it is in Hawaii) it produces undersea volcanoes. Some of these volcanoes build up to the surface of the ocean and become islands. Over millions of years the plate may move across the 'hot spot' and the original volcano become extinct but a new volcano will begin to form in the area of the 'hot spot.'

source of the island

The northwest moving Pacific Plate has moved across the 'hot spot' that created the Hawaiian Islands for millions of years. This movement has left the northwest trending island chain (of over 20 islands and atolls) we call Hawaii. As islands move northwest, away from the 'hot spot,' they begin to erode and become volcanically inactive. Over time the island may erode so much it is no longer an island but an underwater seamount. Kauai is the oldest of the main Hawaiian Islands now, having formed some 5 million years ago, with its volcano considered to be extinct and fully in the process of erosion. Oahu is next, its volcanism is considered to be inactive. Then Maui with its Haleakala crater that could still come to life one more time. And the youngest island is the 'Big Island' of Hawaii itself, with surface lavas all less than one million years old. It still has active volcanism. On the seafloor 20 miles to the southeast of Hawaii is an active volcanic area with periodic eruptions. This area is called Loihi and will be the site of the next Hawaiian Island if geologic processes continue as they have for millions of years but it may be over 10,000 years before this happens.

Hawaiian Island chain

Hawaii's volcanoes

There are five active volcanoes in Hawaii. They are:
Loihi
Kilauea
Mauna Loa
Hualalai
Haleakala

Kilauea is considered one of the worlds most frequently active volcanoes. If you just look at the number of Kilauea eruptions recorded since Europeans arrived, there have been 62 eruptions in 245 years, which comes out to 1 eruption every 3.95 years. However, this completely ignores the fact that some of the eruptions lasted a long time. For example, the current eruption started in January of 1983 and has been continuous ever since! Likewise, there was an active lava lake in the summit caldera from at least 1823 until 1924, while at the same time eruptions would take place elsewhere on the flanks of the volcano.

Lava from Kilauea volcano pouring into the sea. Big Island of Hawaii

Kilauea Caldera, Volcanoes National Park, Big Island of Hawaii

Mauna Loa is an active volcano and is due for an eruption. Mauna Loa has erupted 15 times since 1900. These eruptions have lasted from a few hours to 145 days. Since 1950 Mauna Loa has erupted only twice, in 1975 and 1984. The 1975 eruption lasted 1 day. The 1984 eruption lasted 3 weeks. Nearly all the eruptions begin at the summit. About half of these migrate down into a rift zone.

Haleakala began growing on the ocean floor roughly 1-2 million years ago. It erupted most recently in 1790 at La Perouse Bay.

Hualalai is an active volcano. The resort town of Kailua is on the southwest flank of the volcano. Hualalai last erupted in 1801 and sent lava from a vent on its northeast rift down to the ocean. Swarms of earthquakes in 1929 were probably the result of magma movement within the volcano but there was not an eruption. Hualalai is monitored by geologists of the U.S. Geological Survey’s Hawaiian Volcano Observatory. In the last 24 years there have been no swarms of microearthquakes nor any harmonic tremor. Since the early 1980’s the geologists have been surveying the volcano. Hualalai is not expanding at the present time nor has expanded since the geologists began making their measurements. If anything changes I’m sure we’ll hear about it.

Lo’ihi means “long one”, a reference to its elongate shape. For a 3-d image, check out the Hawaii Undersea Geological Observatory (HUGO) home. Right now, the summit of Lo’ihi is about 970 meters below sea level. It is growing on the lower flanks of its two neighbors, Kilauea and Mauna Loa, with its base at a depth of about 4000 meters below sea level, so you can say that Lo’ihi itself is about 3000 m high. We don’t really know when it will reach the surface or even if it will. There is an underwater volcano off the NW coast of the big island of Hawai’i named Mahukona, and there is debate about whether it ever grew above sea level, or died out prior to doing so. The most often-heard time required for Lo’ihi to reach sea level is about 10,000 years, but that is really only a guess. It might be 30,000 years for all we know. It is far enough away from the coastline of Hawai’i that I imagine that at first it will be a separate island when it breaks the surface. As it grows (and especially if Kilauea and Mauna Loa are still erupting) it will soon be joined to the island.

photos from Hawaiis islands