Lōʻihi Seamount

Map of Loihi off the island of Hawaii

Loihi (also Lo'ihi, Loihi ) is a submarine volcano 35 km south of Hawaii. The height from the bottom of the Pacific Ocean to the summit is about 3000 meters, to sea still missing 975 m.

Near the summit of Loihi is an undersea automatic observatory, which has already observed an outbreak acoustically. A copper and fiber optic cable connects the observatory with the other station at Whittington Beach Park in the south of Hawaii.

Geology

The Loihi is a seamount or submarine volcano, which has its location on the slopes of Mauna Loa, the largest shield volcano on earth. He is the youngest formed by the hotspot under Hawaii volcano and part of the elongated Imperator - back. The distance between the top of the older Mauna Loa and the summit of Loihi is about 80 km and is thus roughly the diameter of the Hawaiian hotspot. The Loihi summit consists of a shaft with three craters, an 11 -km-long fault zone that extends from the summit in a north-south direction, and a 19 km long fault zone, which runs from the summit to the south- southeast.

The shaft craters are named West Crater (English, West Pit '), East Crater (English, East Pit ') and Pele's crater (English, Pele 's Pit '). Pele's crater is the youngest of the three and is located in the southern part of the summit. Its walls are 200 meters high and taken in July 1996, when the hydrothermal vent field Peles (English, Peles Vent ') - collapsed in itself - the formation that was previously in place. With a thickness of 20 m, the walls of Pele's crater are unusually thick for a Hawaiian volcano and suggest that the craters have been filled in the past by lava.

The running from north to south fault zones of the volcano Loihi give the characteristic elongated shape, from which its name (Hawaiian: , long ' ) is derived. The northern fault zone consists of a longer and a shorter western part of the eastern part. Studies have shown that both have the northern and the southern fault no sedimentary cover. This suggests that there was in the recent past there volcanic activity. A bulge in the western part of the northern fault zone has three 60 to 80 m high, cone -shaped elevations.

Until 1970 it held the Loihi for an inactive volcano, which was passed through the sea floor spreading at its current location. The seabed beneath Hawaii has an age of 80 to 100 million years ago and was established on the East Pacific Rise, a divergence zone on the forms by the drifting apart of tectonic plates and rising magma from the mantle of new seafloor. This newly formed crust moves slowly away from the divergence zone. The seabed under Hawaii wandered so over a period of 80 to 100 million years ago from the East Pacific Rise from 6000 km to the west and moved the old seamounts doing with it. However, when scientists in 1970 investigated a series of earthquakes in Hawaii, they found that there is an active volcano in the Emperor Ridge at Loihi. The age structure of the crater on its summit confirmed that the Loihi moves slowly eastward due to volcanic activity and from its origin above the Hawaiian hotspot.

From the seabed measured from the Loihi has a height of more than 3000 m, but its peak is still 975 m below the water surface. The Loihi has a slope angle of about five degrees. Its northern foot begins about 1900 m below sea level on the slopes of Mauna Loa, while the south side rests on the seabed and with 4755 m is much deeper below sea level. From the north side measured his summit therefore is 931 m above the sea floor, but from the south side of the volcano measured reaches a height 3786 m above the sea floor.

The Loihi follows the typical for Hawaiian volcanoes development scheme. Geochemical analyzes of its lava show that the Loihi is currently in the transition phase from pre- shield stage to shield volcano and provides us with valuable clues about the early evolution of Hawaiian volcanoes. In the pre- shield stage of these volcanoes have steeper slopes, a low level of activity and promote alkaline basalt. Other volcanic activity of the Loihi will eventually form an island. The growth of the volcano has led to a destabilization of its side slopes. That's why it comes info Frequently landslides and much of the steep southeast slope is covered by scree. Similar deposits at other Hawaiian volcanoes show that such debris from landslides is typical of the early development of a Hawaiian volcano. It is expected that the Loihi will rise in 10,000 to 100,000 years above sea level.

Age and growth

Using the radiometric dating of the age of rock samples from the Loihi was determined. The Hawaiian Center for Volcanology [dt. Hawaii Center for Volcanology ] investigated rock samples were collected during various expeditions. Here is the 1978 guided expedition, are from the 17 taken with a towing backhoe samples of particular importance. Most of the samples proved to be old: the oldest rock dated to circa 300,000 years. According to the seismic activities in 1996 also some young breccias were collected. Based on the rock samples, scientists estimate the age of the Loihi to about 400,000 years. Some samples from the active eastern side of the volcano have been dated to 4000-21000 years this data being but are not considered reliable. At the foot of the volcano forms an average of 3.5 mm per year and a new rock near the summit 7.8 mm per year. If the data model of other volcanoes like Kilauea is transferable to the Loihi can be assumed that 40 % of the volcanic mass has formed during the last 100,000 years. Assuming a linear growth, would have the Loihi an age of 250,000 years. However, since the activity of the Loihi has increased over time, as is typical for hotspot volcanoes, it takes at least 400,000 years before a volcano of this type reached the mass of Loihi. The Hawaiian volcanoes are moving at a speed of about 10 cm per year to the northwest. This means that the Loihi located 40 km south-east of its present location was on his first outbreak.

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