Vailuluʻu facts for kids
Quick facts for kids Vailuluʻu |
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Location of American Samoa
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| Summit depth | 590 metres (1,940 ft) |
| Height | 4,200 m (13,800 ft) |
| Location | |
| Location | South Pacific Ocean |
| Coordinates | 14°12′54″S 169°3′30″W / 14.21500°S 169.05833°W |
| Country | United States |
| Geology | |
| Last eruption | 2003 |
| History | |
| Discovery date | 1975 |
Vailuluʻu is an active underwater volcano, also known as a seamount. It was discovered in 1975. This volcano rises from the ocean floor and its top is about 593 m (1,946 ft) below the surface of the water.
Vailuluʻu is located in the Pacific Ocean. It sits between the islands of Taʻu and Rose. Scientists believe it is the current spot of the Samoa hotspot. This is a place deep in the Earth where hot rock rises. The top of Vailuluʻu has a large, oval-shaped crater. This crater is about 2 kilometers (1.2 miles) wide and 400 meters (1,300 feet) deep.
Volcanic eruptions at Vailuluʻu were recorded in 1973. In 1995, many earthquakes happened, which might have been from an eruption. Hot water plumes rise from the volcano's top. This shows that the volcano is still active. If Vailuluʻu keeps erupting, it might one day grow tall enough to become a new island.
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What's in a Name?
The seamount was first found in 1975. At first, it was called Rockne Volcano or Fa'afafine seamount. In 2000, Samoan high school students gave it the name Vailuluʻu. This name refers to a special rain that was said to fall when the last king of Samoa gathered his people.
A cone inside the volcano's crater is named Nafanua. This name comes from a Samoan war goddess, Nafanua. Today, Vailuluʻu is part of the National Marine Sanctuary of American Samoa. This means it is a protected area.
Where is Vailuluʻu Located?
Vailuluʻu is east of American Samoa. The island of Ta'u is about 43 kilometres (27 mi) west of Vailuluʻu. Other nearby seamounts include Malumalu Seamount and Rose Atoll.
Vailuluʻu is shaped like a cone. Its deepest part is about 593 metres (1,946 ft) below the sea surface. The crater at its top is 2 kilometres (1.2 mi) wide and 0.4 kilometres (0.25 mi) deep. The shallowest part of the seamount is on the western edge of this crater.
The seamount looks like a star from above. It has two main ridges extending east and west. A smaller ridge goes to the south. The volcano is huge, about 1,050 cubic kilometres (250 cu mi) in size. Its height above the seafloor is similar to large mountains on land, like Fuji. The seafloor around Vailuluʻu is about 5 kilometres (3.1 mi) deep.
A cone named Nafanua grew inside the crater in 2004. This cone is about 300 metres (980 ft) tall. Before Nafanua formed, the crater had several smaller holes. The Nafanua cone is mostly made of pillow lava, which looks like stacked pillows.
Hot Water Vents
Hot water vents, called hydrothermal vents, are found in the crater. Some vents release very hot water, up to 80 °C (176 °F). Others release cooler water, around 20 °C (68 °F). This hot water makes the water inside the crater cloudy and warmer than the surrounding ocean.
The hot fluids from these vents are rich in sulfides. Tiny droplets of carbon dioxide have also been seen. These vents can make the water so cloudy that you can't see more than 2 metres (6 ft 7 in) underwater. The hot water mixes with the cold seawater in complex ways.
A lot of water flows from these vents, about 0.13 cubic kilometres per day (1,500 m3/s). The total power of this hot water system is very high, like 610-760 megawatts. This creates large plumes of hot water that spread out from the volcano.
How Vailuluʻu Formed
Vailuluʻu is at the eastern end of the Samoan volcanic chain. Scientists believe it is the current location of the Samoa hotspot. This idea comes from the volcano's position and the types of rocks found there.
The Samoa region is near the Tonga Trench. This is where the Pacific Plate is sliding under another plate. This movement might explain why older islands in Samoa still have recent volcanic activity. However, the islands generally get older as you go west. This suggests they formed over a hotspot, like a conveyor belt moving over a fixed hot spot.
The rocks found at Vailuluʻu are mostly alkali basalts and picrites. These are types of volcanic rocks. The volcano's rocks show signs of being changed by hot water. For example, quartz has been found in rock samples.
The hot vents also create chimneys made of iron oxide. These chimneys can be from a few centimeters to several meters tall. These areas might even be targets for future mining because of the minerals they contain.
Life Around the Volcano
Many different bacteria live on Vailuluʻu. They form microbial mats on the rocks. These bacteria are similar to those found on other underwater volcanoes around the world. Various types of yeasts and other fungi have also been found. They might play important roles in the volcano's ecosystem.
These microbial mats can be 2–4 centimetres (0.79–1.57 in) thick. They often contain deposits of iron hydroxide and iron oxide. Microorganisms here might use sulfur, manganese, and iron for energy.
Many animals also live on Vailuluʻu. Demosponges are found in the crater's openings. Crinoids, gorgonians, ophiuroids, and sponges live on the western ridge. In areas without hot vents, echinoderms, octocorals, and sponges are common.
Crabs, eels, and octopuses have been seen near the summit. The eel populations are so large that part of the volcano is nicknamed "Eel City." These eels eat small crustaceans carried by ocean currents.
Life is different in various parts of the volcano. The summit of Nafanua has plenty of oxygen and food, attracting eels. However, the crater floor is called the "moat of death." This is because there is very little oxygen there. Polychaetes, a type of worm, feed on dead fish found on the crater floor.
When Did Vailuluʻu Erupt?
Vailuluʻu is an active volcano. It has frequent earthquakes, volcanic eruptions, and hot water activity. On average, about 4 earthquakes happen here every day. This is unusual for this part of the Pacific Ocean.
Large groups of earthquakes, called seismic swarms, happened in 1973, 1995, and 2000. The places where these earthquakes start seem to be connected to the hot water areas and the volcano's southeastern ridge.
Studies of rocks from Vailuluʻu show it has been active for the last 8,000 years. Eruptions inside the summit crater have happened in the last hundred years. Rocks collected from the volcano have been very young, some less than ten years old.
The 1973 seismic swarm was likely a major underwater eruption. The most recent eruption, between 2001 and 2004, was not seen directly. This eruption formed the Nafanua volcanic cone inside the crater. If eruptions like this continue, Vailuluʻu could eventually rise above the sea. Because its summit is not very deep, powerful explosions could happen. These might affect nearby coastal areas and ships.
Gallery
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The summit of Nafanua is covered with thick microbial mats, showing low-temperature hot water vents.
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Broken pillow lavas, colored red by iron oxide, inside Vailulu'u crater.
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An octopus living on the western summit of Vailulu'u.
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Swimming elasipod sea cucumber, Paleopatides sp., photographed off the northern shore of Tau Island, Vailulu'u Expedition 2005.
