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Mauna Kea (left) and Mauna Loa (center distance) of the Big Island of Hawaii. The cliffs of the Pololu Coast are in the foreground. They don't look it, but these two mountains are more than 13,000 feet above sea level, and measured from the seafloor are two of the biggest mountains on planet Earth
The MJC Geology crew, an intrepid group of 27 explorers, completed an expedition to the Hawaiian Island in June of 2009. We were studying the geology, of course, but we were also interested in the other aspects of the natural and human history of the islands too. We spent a week on the Big Island of Hawaii, with four days near the active volcanoes, and three days on the Kona-Kohala Coast. We then flew to Kaua'i for three days, and then Maui for the final three days.
The trip was planned so as to see the different stages in the development and destruction of the great shield volcanoes that make up the islands. Geologic time is truly compressed on the islands, as each island tends to disappear beneath the waves after a geologically short time of 6-7 million years. The islands have their origin in a hot spot, or mantle plume, which is a very hot region of upwelling magma deep in the earth's mantle that melts its way to the seafloor, building up a volcanic pile that after thousands of eruptions emerges above the waves.
The volcanic masses are heavy and push down on the seafloor crust, and the islands start to sink even as they continue to erupt and build. As the volcanoes are carried off the hot spot, the volcanic fires die as well, and the islands are ultimately doomed to disappear under the relentless grinding of erosional forces.
The volcanoes go through three main stages of development before they are destroyed: a shield building stage, an alkali basalt capping stage, and following a period of dormancy, a sort of last-gasp rejuvenation stage. Then they go extinct forever. 400 miles to the northwest of Kaua'i, there are two small towers of rock called the Gardner Pinnacles. Covering less than six acres, the 170 foot high rocks are the last small remnant of an island that used to rival the Kaua'i or Maui. It will be gone in a few thousand years. It represents the fate of all the Hawaiian Islands, even as new islands are gestating beneath the waves. Loihi, southwest of the Big Island and 3,000 feet below sea level, will be the next island in a few tens of thousands of years
A Photojournal of our Expedition (follow the links to each island)
| Hawai'i, The Big Island: the Active Volcanoes | Hawaii, the Kona Coast and the Old Volcanoes |
| Kaua'i, The Garden Island | Maui, The Valley Island |
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