# Volcano Watch — Treasures of the Deep Sea: Loihi Hosts Hydrothermal Vents

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Energy from the sun supports most life on our planet, but far below the sea surface, another, less obvious energy source pumps heat and life-giving energy into the earth's biosphere. As a result, life persists independent of the sun's energy in some special seafloor environments.

Crabs, giant clams, and oversized tubeworms are among the strange critters able to live in these most remote recesses of the deep sea, receiving no sunlight and virtually no nutrients from the world above. Instead, these seafloor dwellers survive on heat energy coming from the earth's molten interior. In this unusual setting, the base of the food chain is supported by "chemosynthetic" microorganisms rather than the photosynthetic plants that most of the earth's biota depend upon for food. Instead of using the sun's radiant energy, chemosynthetic organisms use the chemical energy present in superheated fluids that spew out of the ocean floor. These jets of hot fluid issue from what are known as "hydrothermal vents."

Hydrothermal vents form where seawater percolates down through fractures in the oceanic crust, heating up as it descends toward the earth's hot interior. This hot seawater interacts with the crust along its downward flow path, removing certain chemicals from the rocks. In fact, the interaction with the crust alters the fluid composition and temperature so much that the fluid is no longer considered seawater but "hydrothermal fluid."

Once the hydrothermal fluids are hot enough, they become extremely buoyant and rise quickly through passageways in the crust until finally the hot, mineral-rich fluid shoots up through the seafloor into the ocean. The fluids can be as hot as 350-400o C (660-750o F). This is four times hotter than a pot of boiling water, but the extremely high pressure prevents the fluids from boiling. The chemicals dissolved in the fluids promptly precipitate around the jet of hot fluid as it exits the seafloor and chills in the near-freezing ocean bottom waters.

The minerals that form at hydrothermal vents tend to make chimney-like structures that surround and insulate the jet of fluid. Hydrothermal chimneys are irregularly shaped structures that resemble the hornitos that form at Puu Oo on Kīlauea. High-temperature hydrothermal minerals can be quite beautiful and include colorful and shiny minerals like bornite, also known as "peacock ore" for its blue-green iridescence. Even gold and silver have been found, but pyrite or "fool's gold" is much more common.

Hydrothermal vents form near most submarine volcanoes. Researchers discovered the first hydrothermal vent in 1977 about 400 km (250 miles) northeast of the Galapagos Islands. Most vent deposits are a few meters tall, but one chimney off the Oregon coast reached the towering height of a 15-story building and was dubbed "Godzilla." Hydrothermal deposits have even been found in some lakes in Africa where the continental crust is hot and thin, as it is in the oceans.

In Kīlauea's backyard, a number of hydrothermal vents decorate the summit of Loihi seamount. Loihi is located about 30 km (20 miles) off the southeastern shore of the Big Island and is the youngest volcano in the Hawaiian chain, still submerged under 1,000 m (3,200 feet) of water. In the 1980s low-temperature hydrothermal activity was first observed on the summit of Loihi, where vents emitted fluids with a temperature of about 30o C (85o F). In 1996, however, major seismic and eruptive events led to the collapse of Loihi's summit area, forming a crater called Pele's Pit, roughly the size of Halemaumau Crater at the summit of Kīlauea. This activity wiped out the original vents, but new ones dubbed "Lohiau" and "Forbidden" emerged soon thereafter.

Interestingly, after the 1996 events, the new vent fluids were slightly higher in temperature than their predecessors, at about 80o C (175o F). Late the following year, the venting fluids had increased to more than 200o C (400o F), causing high-temperature, lustrous metallic minerals to form. These gleaming, new hydrothermal chimneys must be highly prized treasures in the undersea annex of Pele's volcanic realm.

### Volcano Activity Update

Eruptive activity at the Puu Oo vent of Kīlauea Volcano continued unabated during the past week. Surface flows are mainly confined to Puu Oo crater and the area immediately outside of the crater in the vicinity of the West Gap section of the cone. Leaks from rootless shields near the top of the Mother's Day tube system feed short flows. Occasional breakouts from the Kohola arm of the Mother's Day flow occur at the top of Pulama pali. The east side of the Mother's Day flow, and the coastal flat below Paliuli, continue to be dark. No lava is entering the ocean.

One earthquake was reported felt in the week ending on November 13. A resident of Ocean View Estates subdivision felt an earthquake at 5:10 p.m. on Friday, November 7. The earthquake responsible was a magnitude-3.1 event located 41 km (24.5 mi) south of Kalapana at a depth of 52 km (31.2 mi).

Mauna Loa is not erupting. The summit region continues to inflate. Seismic activity remains very low, with only one earthquake located in the summit area during the last seven days. Visit our website (hvo.wr.usgs.gov) for daily volcano updates and nearly real-time earthquake information.