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Loihi seamount, sometimes known as the "youngest volcano" in the Hawaiian chain, is an undersea mountain rising more than 3000 meters above the floor of the Pacific Ocean (Loihi is the red-capped nub that is pointed out in the of the image above). Both Loihi and Kilauea volcanoes sit on the flank Mauna Loa volcano, an older, larger, and still active volcano on the Big Island of Hawaii. Loihi sits submerged in the Pacific off of the south-eastern coast of the Big Island of Hawaii (this is the grey area labeled "Hawaii" at the top of the image). Although hidden beneath the waves, Loihi is nevertheless taller than Mt. St. Helens was prior to the catastropic volcanism there in 1980.
Before to the 1970's, Loihi was not known to be an active volcano. Instead, it was thought to be a fairly common old seamount volcano of the type that surrounds the Hawaiian islands. These latter volcanoes are similar in age (80-100 million years old) to the sea floor upon which the Big Island of Hawaii sits. This sea floor was itself created some 6000 km away on the undersea volcanic mountain chain known as the East Pacific Rise. It has slowly moved north-westward to the present location of the Hawaiian Hotspot.
In 1970, our ideas about the seamount changed drastically following an expedition that went to Loihi to study an earthquake swarm (intense, repeated seismic activity) that had just occurred there. It was revealed that Loihi was a young, active volcano, rather than an old dead seamount from a bygone aeon. The volcano is mantled with young and old lava flows and is activly venting hydrothermal fluids at it's summit and south rift zone. In August 1996 Loihi volcano rumbled to life again with a vengence and has been intermittantly active since then (as described below and elsewhere at this web site). In fact, University of Hawaii scientists studying the seamount following the 1996 seismic swarm have found direct evidence of a volcanic eruption there in 1996, making this the first confirmed historical eruption of the seamount. Loihi shares the Hawaiian hot spot with its larger active siblings Mauna Loa and Kilauea.
A Tour of Loihi: The Summit Region
This is a 3-D bathymetric map of the southernmost 2/3 of the Loihi summit platform. Three pit craters are the most distinctive features. The southwesternmost crater is a new feature formed during the 1996 seismic event. This crater, named Pele Pit, is roughly 300m deep. It formed in a location that was previously the high-point on the summit, the old Pele's vents area of hydrothermal activity. Adjacent to the New Pit was a breccia field of both fresh and altered pillow lava fragments.
Life around the summit:
The scientific name of this curious looking fish is Sladenia remiger. It is common on the summit of Loihi.
A Tour of Loihi: The New Summit Pit Crater
This is a 3-D bathymetric map of the new Pit Crater formed during the 1996 seismic event. The crater is roughly 300m deep and formed in a collapse event. It is located in a site that was previously the high-point on the summit, the Pele's vents area of hydrothermal activity. Notice the very "rough" nature of the topography on the pit's walls. The pinnacles on the western side of the pit are near vertical spires of material left behind during the pit collapse and have been observed from the Pisces V submersible to be quite precarious.
Since the pit collapse, hydrothermal activity has resumed in the the pit, forming new chimneys of minerals built up at the places where these fluids issue onto the seafloor. Activity is occurring in at least 2 sites, Lohiau vents (the left "x" in the image above and Forbidden vents (the right "x" in the image). Exit emperatures of over 200 °C have been recorded within the Forbidden vents chimney's chimneys. Get more details on the HCV-Loihi Hydrothermal Vents page. This vent had, within the course of a year, spawned new hydrothermal chimneys comprised mostly of Pyrite and Barite (see below). You can view additional images of these hydrothermal minerals at: www.mbari.org/~davisa/Loi.hydrothermal2.html
A Tour of Loihi: The HUGO Site
Anyway if you want to take a tour of the remaining area's click HERE
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