Tuesday, July 6, 2010

Five Volcanoes !

All Hawaiians know the Big Island was created by the commingling lava flows from five immense volcanoes, but most visitors know only two – i.e., Mauna Loa and Mauna Kea.  And, somewhat uniquely, the volcanoes of Hawaii are not where plates meet, but actually thousands of miles from the nearest plate boundary in what is known as a “hot-spot” in the Pacific Plate.  Also, Hawaii’s volcanoes are not the type like Mt. St. Helens or Mt. Etna that can have explosive eruptions; they simply release flows of relatively fluid lava.

Currently there are two volcanoes on the Big Island classified as active:

1.   Kilauea, actively erupting for almost the past 30 years is the world’s most active volcano.  It has been spewing lava continuously since January 1983.   Kilauea nestles into the side of Mauna Loa and was once considered a part of Mauna Loa, but subsequent research showed that it has its own “magma-plumbing system.”  http://hawaii.aloha-hawaii.com/hawaii/big+island+volcanoes/

Located in Volcanoes National Park near the caldera of Kilauea is the “fire pit,” which is known as Halemaumau (“House of Everlasting Fire”).  Halemaumau at times has a contained lake of boiling lava. The pit is enlarged periodically by steam blasts and collapsing walls. Typical eruptions consist of lava flows forming lava lakes in Halemaumau or elsewhere on the caldera through fissures and rift zones.  Volcanoes National Park is actually Hawaii’s most visited tourist attraction, with nearly 9,000 daily visitors coming to the park. http://www.hawaiilogue.com/active-volcanoes-in-hawaii.html

Pele, the Hawaiian Volcano Goddess, is said to live within the Halemaumau firepit.

2.   Mauna Loa (“Long Mountain”), which last erupted in 1984 is the world’s largest volcano. It is also considered one of the most active volcanoes, having erupted 33 times since 1843.

Both of these active Hawaiian volcanoes share the Hawaiian hot spot, but retain unique volcanic histories and compositions.

And three volcanoes on Hawaii are generally classified as dormant:

1.   Kohala, the oldest, which is believed to have emerged from the sea more than 500,000 years ago.

2.   Hualalai, with six different vents that spewed lava, two of which produced lava flows that reached the ocean. The Kona International Airport is build atop the larger of the two flows. It last erupted in 1801, but some still consider it still “active,” which would be a major problem for the population center around Kona-Kohala.

3.   Mauna Kea (“White Mountain”), reaching 13,796 feet above sea level is the world’s tallest mountain (measured from the floor of the ocean to its summit) which last erupted about 4,000 years ago.  It is often snow covered in winter.  It is also the site of 13 astronomical observatories and is expected to be home to what will be the world’s largest telescope, the Thirty Meter Telescope.

Since the vast majority of earthquakes and volcanic eruptions occur near plate boundaries, how did the Hawaiian Islands which are entirely of volcanic origin, form in the middle of the Pacific Ocean almost 2,000 miles from the nearest plate boundary?

“J. Tuzo Wilson came up with the Hotspot Theory in 1963. According to his theory, the Hawaiian Island chain resulted from the Pacific Plate moving over a deep, stationary hotspot in the mantle, located beneath the present-day position of the Island of Hawaii. Heat from this hotspot produced a persistent source of magma by partly melting the overriding Pacific Plate. The magma then rises through the mantle and crust to erupt onto the seafloor, forming an active seamount.

Over time, countless eruptions cause the seamount to grow until it finally emerges above sea level to form an island volcano. As the plate movement carries the island beyond the hotspot, the magma source is cutoff, and volcanism ceases. As one island becomes extinct another develops over the hotspot.”  http://www.pdc.org/iweb/volcano_history.jsp

In fact right now a young submarine volcano called Loihi (“Long”) is growing about 20 miles south of the Big Island.  Its ascending summit is currently 3,000 feet below the ocean surface.  http://www.bestplaceshawaii.com/island_insights/bigisland/volcanoes.html

When most people envision a volcano, they think of a tall and cone shaped volcano (think Mount Hood outside of Portland, Oregon). These strato volcanoes tend to have dramatic and explosive eruptions (think Mount Saint Helens).

The five volcanoes of the Big Island are shield volcanoes, which are long and broad and have gently sloping hills.  Shield volcanoes’ lava has a lower viscosity, meaning that the lava is thinner and more fluid.  Because of the fluidity of the lava, major explosive eruptions generally do not occur.  This is why the almost constant flowing lava of Kilauea can be approached and seen by visitors to Volcanoes National park. http://www.hawaiilogue.com/active-volcanoes-in-hawaii.html

All the photos in this post are by Bryan Lowry, are © protected and usage requires his permission.  Please visit Bryan‘s website to see the vast collection of images by this award winning photographer whose photos have also appeared in National Geographic (http://lavapix.com). Significantly, 20% of Bryan’s website sales profits go to Easter Seals Hawaii on the Big Island.

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Mahalo for leaving a comment!~WesIsland