There are 100 islands in the Hawaiian Chain. However, most of the land mass is concentrated in the Easterly most islands,the ones which people are most familiar with. The Westernmost of the islands of the chain are the Midway and Kure Atolls. If one is interested in geology, one can travel westwards on the Hawaiian Chain and see the progression of the ages. The form of aging most often associated with the Hawaiian Islands is erosion. On Kure and Midway erosion has made the islands into atolls. On the oldest main Hawaiian Island, Kauai, erosion is plainly visible. Wonders like the Waimea Canyon show what erosion can do. The newest island, the island of Hawai'i, is the most unstable and still volcanically active. It is still growing.
Hawaii is volcanic in origin, as many of you may know. It is located over a “Zone of Weakness”, otherwise called a “hot spot” situated on the ocean floor, on the Pacific Plate. As a matter of fact, the study of the Hawai'ian islands has made a big contribution to the study of Plate Teutonics. Magma pushes up against the mantle, and the pressure becomes so great that a crack, or fissure, is formed through the crust. Magma flows out of this and accumulates over a very long period of time to make an island. The entire Pacific plate is moving northwest at a steady pace, but the hot spot stays in the same place relative to the earth. After enough lava has accumulated over thousands of years, the area over the hot spot will close. A few miles later the hot spot might open again, making a new island. The Hawaii Islands were formed by a 1600 mile long fissure, 25,000,000 years ago. The surface area of Hawaii represents the mere tip of gigantic sea mountains.
The Hawaiian hot spot is still active, and there is a new seamount, called Loi'hi that will eventually become part of the Big Island. Studying Lo'ihi has give scientists an opportunity to understand the formation of a volcano in the pre-shield stage. Volcanoes have several distinct phases that they go through while becoming a shield – all the Hawai'an Islands are shield volcanos. The initial structure of a Hawai'ian volcano is believed to be a cone with steep sides, this is called the pre-shield phase. During the pre-shield phase the volcano begins developing rift zones. These developed into major sources of lava. After the pre-shield phase, its eruptions become more frequent and it produces more and more lava. The flows spread out, pile on top of each other and the shape changes from a steep cone to a shield, whose sides run at a shallower angle. Most of the Hawaiian islands were in the shield building phase when they broke the surface. By the time a major Hawai'ian volcano nears the end of its shield building phase, its top can be thousands of feet above sea level. Mauna Loa is believed to be near the end of its shield building phase. Kilauea is still in its shield building phase, with active eruptions. After this is completed, erosion begins its quest to reduce the island to a memory. The ocean pounds the cliffs, slowly making the island smaller, while rain creates valleys while washing away the ground. Additionally lava flows on to of lava, and the union of these flows is weak. Lava also contains many air pockets and tubes, and these become more and more unstable as more and more lava is piled on top. These massive amounts of rock will slowly collapse, sinking the summits underneath the seas once again.
There are three types of lava commonly seen in Hawaii. Aa Lava flows are composed of dense basalt with stretched and irregular vesicles. Pahoehoe lava congeals with a relatively smooth, pillowy and entrail-like surface. Pillow lava is the rarest. It occurs when Pahoehoe lava flows over a moist surface. This kind of lava is spheroidal and usually flattened on the underside. One finds this kind of lava mostly under water. As a matter of fact, it is thought that the whole submerged part of the Hawaiian Islands is made up of pillow lava.
Each of the volcanos has several vents, and most of these are now calderas. Calderas are large bowls shaped volcanic depressions more than a kilometer in diameter and rimmed by in facing cliffs. Calderas are mostly formed by the collapse of the top of a volcano because of the removal of the support of the magma reservoir. After the collapse, the top of the volcano has disappeared, replace by a gaping hole in the earth.
Lava and Lava Phenomenons
In most countries, an eruption is something you want to be as far away from as possible, but on The Big Island, people stop whatever they are doing and come to see eruptions and active lava flows. While most volcanoes erupt in huge clouds of ash, Kilauea dribbles and drools, moving most of its lava underground. Occasionally, it will spew molten lava in huge fountains hundreds of feet tall, but this has only happened twice in recorded history. Most of the lava coming out of Kiluea is Pahoehoe, but there are some A'a flows. Lava from Kilauea does not come from a single spot, instead it changes, flowing from several different vents. The current one is Pu'u O'o, which has been erupting since1983. It materialized just inside the park boundary. In 1990, the town of Kalapana was completely buried. The lava flow was slow enough that everyone was evacuate in time.
One of the most spectacular events that ever happened with Kilauea was the lava lake at Kiluea Iki (meaning little Kiluea). In 1959, scientists detected that there would be an eruption in Kiluea, so they set up their instruments at Halemaumau because that had been the spot that had been active. They were completely surprised when it erupted a mile away in Kiluea Iki. Ground zero was Pu'u Pua'i, meaning Gushing Hill. Huge fountains of lava, some up to 1,900 feet high, spew out enough to cover a football field with 15 feet of lava every minute! After a while, the vent would stop spewing lava, and the pool would drain out the bottom and feed the fountain again. When it was over, 39 days over there was a bathtub ring of lava to show how high the lava had gotten. When papa saw this he made up an advertisement. “Do you have lava rings on your crater? Now you can remove these troublesome rings with the new “Lava Off “ TM. Call now and get 25% percent off!” The hike through the crater is one of the best on the Islands, showing the contrast between lifeless void and lush rain forest. My first look at a crater did not impress me. But then I took in the details and realized that it was three miles across and at least 600 feet deep.
Most of Kilauea's flows are located not on the surface, but underground in tubes. When lava travels through these tubes, it only loses 20 degrees of its temperature. One thing that most people don't think about how hot lava really is. When we walked to see the lava flowing into the ocean, Nikki became faint with heat. It is extremely, unbelievably hot. Lava behaves always differently and you never know what you will encounter during your stay.
Climate Zones in Hawaii
Hawaii in general has 5 major climate zones, Beach,
Native Forests, Wetlands, High Bogs and Tundra.
1. The beach area is mostly shrubby or herbaceous, with nothing over 3 feet tall.
2. The native forest is mostly rain forest, but there are some normal ones. Banyan are some of the most majestic trees in this area. The forest is inhabited by many things, but the most notable are the Honeycreepers. These are bright birds that make high pitched peeps.
3. The Wetlands include rivers and streams. Birds are the most numerous here (asides from fish). One of the birds here, the Mudhen, is endemic to Hawaii. It is black and has a red bill.
4. The most interesting of the zones are the High Bogs. As far as I know, these are only on Kauai. They are swamps teeming with plant life. As the name suggests, these are mostly located up high.
5. The tundra is only located on the top of Mauna Kea. There is almost no life here, except for the odd beetle, as the air is to thin and frigid for most animals.
All over the climate zones, endemic plants and animals have developed intricate co-dependancies. One of the most interesting endemic plants is the Ilian. It is a member of the sunflower family and only grows on the dry mountain slopes of Kauai. It takes several years to bloom, and after it blooms the plant dies. When in bloom, the plant looks like a gigantic pineapple.
Hawaii has the most divers climates of any state in the USA, maybe even the world.