Thursday, February 19, 2009

10 Incredible Underwater Volcanoes

Did you know that Hawaii’s Mauna Kea or White Mountain is the world’s tallest peak, measuring 16,400 m (47,000 feet) from base to summit? And that underwater volcanoes account for 75% of annual magma output? Just like Mauna Kea’s height, with 10,000 m (33,500 feet) under sea level, underwater volcanoes and their eruptions often go unnoticed. And because the usual signs like rumbling and smoke are harder to detect, it is all the more spectacular when an underwater volcano visibly erupts. Follow us around the globe for some of the most stunning sights.

It is estimated that there are currently 5,000 active underwater volcanoes worldwide; of various sizes, standing alone or forming ridges with other volcanoes, of which the highest ones will rise above the surface as islands. The submerged part of the Hawaiian Islands, for example, is one of the largest and longest volcanic ridges – more than 2,400 km (1,500 miles) long.

As underwater fissures in the earth’s surface, most submarine volcanoes are located near areas of tectonic plate movement. Clusters of terrestrial volcanoes therefore point to hotbeds of underwater volcanic activity as well, like the places portrayed here around Hawaii, California, Iceland, Japan, New Zealand, the Caribbean and Antarctica.

Molokini Crater, Hawaii

Today, Molokini Crater (above) in Maui County, Hawaii is a crescent shaped “island” popular with scuba divers, snorkelers and seabirds alike, but it used to be a fully round, volcanic crater. One can just imagine the underwater volcano in its heyday, forming a few new islands through eruption.

Morro Rock in California is part of a series of volcanic plugs known as the “Nine Sisters,” created over 20 million years ago. The explosion of a submarine volcano created Morro Rock, a giant piece of lava that, once in contact with the sea water, formed a solid crust and settled in the neck of the volcano, similar to a cork resting in the neck of a bottle. Champagne-like explosions are not to be expected as the volcano is not active any more. The rock was named “El Morro” (pebble) by Portuguese explorers in the 16th century when the volcano’s crater was still visible. Today, erosion is constantly shaping Morro Rock.

Morro Rock, CA

The diagram on top shows how a submarine volcano’s lava, ash and debris can settle on top of it, thus raising its peak, often above sea level. Or, a big rock or piece of lava can lodge itself in the volcano’s crater – hopefully after all the pressure has been released!

In some cases, volcanic eruptions form whole new islands, for example the island of Surtsey in Iceland. Here’s the picture of the eruption of an underwater volcano (left) in November 1963 that started 130 m below sea level, and Surtsey today (right). The island, being the youngest, is the ideal study object for geologists, botanists and biologists and has been declared a UNESCO World Heritage Site.

Surtsey being created, Iceland

Iceland is a country that sees sporadic underwater volcanic eruptions. Heimaey, the largest island of the Vestmannaejyar archipelago, had its most spectacular volcanic activity in 1973, when lava from the Eldfell (Mountain of Fire) volcano threatened to block Heimaey’s harbour. The volcano, here seen in the northeast of the island, clearly just looks like the tip of the iceberg – or rather volcano – leaving one to speculate how much more lies beneath.

This is a picture of the eruption of an underwater volcano in the Pacific Ocean near the Japanese island of Iwo Jima in July 2005. A member of the Japanese army stationed on the island had alerted authorities after noticing a 1-km (3,280 feet) column of steam.
Underwater volcano near Iwo Jima island, Japan

Here’s another picture showing the circular eruption and various streams of steam coming out:

Brothers volcano is part of the active Kermadec Arc, 400 km northeast of New Zealand, and lies 1,850 m below sea level. Amazing is the submarine volcano’s 3-km-wide caldera, a large crater caused by a volcanic explosion with 300 to 500-m-high walls, which were formed 37,000 to 51,000 years ago.

3-D diagram of Brothers volcano, Kermadec Arc (400km northeast of New Zealand)

Healy Volcano is another large submarine volcano on the Kermadec ridge:

Probably the most spectacular capture of an underwater volcano eruption was that of the NW-Rota 1 on the seafloor south of Japan in April 2006, when Woods Hole Oceanographic Institution’s (WHOI) undersea vehicle Jason caught the eruption on camera during routine checks. Prior to that day, scientists had never been so close to an erupting submarine volcano, let alone taken audiovisual recordings. Says WHOI expedition leader Will Sellers about the experience:

“There were some scary moments. There was a significant amount of gas coming up out of the pit. You could only imagine what it would have been like at the surface, if it wasn’t under that kind of pressure (from the tons of seawater above). It would have been huge. You wouldn’t have been able to stand anywhere near it. …The common reaction was, ‘Are you sure we should be here?’”

Here’s a video of the spectacular underwater explosion. Notice that the lava in the vent is rising so fast that only a small glimpse of red glow can be seen:

NW-Rota 1, seafloor south of Japan

Kick ‘em Jenny is the name of an active underwater volcano on the floor of the Caribbean Sea, about 8 km north of Grenada. Between 1939, the volcano’s first recorded eruption, and 2001, its last, it is said that there were 12 further eruptions. Today, there is a 5-km safety zone around the volcano to deter adventurous snorkelers and scuba divers.

Kick ‘em Jenny, Caribbean seafloor

Even cold Antarctica is home to volcanic fire. Here is a picture of the Bransfield Strait with Brunow Bay and Livingston Island in the foreground and the Antarctic Peninsula in the background.

Who would suspect that under such a serene surface waits a submarine volcano? Here’s a 3-D perspective of the ocean floor:

And, last but not least, a cool reconstruction of how ships can measure the height and surface area of submarine volcanoes:

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