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Tonga Volcano and Earthquake PDF Print E-mail

Spectacular clouds began spewing out of the sea on Monday about 10km from the southwest coast off the main island of Tongatapu, where up to 36 undersea volcanoes are clustered. I almost had this post finished, when a tsunami watch was issued, due to a 7.9 earthquake in Tonga. The watch was quickly canceled, but certainly generated a lot concern.

Here's audio with John Bellini, from the US Geological Survey, as he told the BBC that the quake had the potential to create a tsunami: Tonga hit by strong earthquake

It's not surprising that this earthquake occurred, considering that there was quite a spectacular event that happened on Monday in Tonga. There were underwater eruptions taking place near the low-lying twin volcanic islands of Hunga Tonga and Hunga Ha'apai, and within sight of the capital, Nuku'alofa. Tonga, which lies almost 2,000 kilometres northeast of New Zealand, lies on the so-called Pacific "Ring of Fire", where continental plates collide causing frequent volcanic and seismic activity.

Hunga Tonga-Hunga Ha'apai (how's that for a name?), a shallow seamount in Tonga, appears to have erupted. 

Huge columns are spewing out of the sea about 10km from the southwest coast off the main island of Tongatapu - an area where up to 36 undersea volcanoes are clustered, geologists said.

New Zealand air traffic is being disrupted by the eruption, and an Airways New Zealand spokeswoman as saying that the volcano’s eruption column is reaching 15,000 metres altitude. Wellington VAAC, however, currently reports ash at flight level 150, which is 15,000 feet. The highest altitude they have reported the emissions reaching is flight level 250, (25,000 feet).

There's a possible connection to a magnitude 4.4 earthquake last Friday, 35km W of Tongan capital Nuku’alofa (quake details from the USGS here). And I guess we can probably assume that today's earthquake is connected as well...maybe we'll see even more undersea eruptions?

Hunga Tonga-Hunga Ha'apai - at least the part above water (look in the bottom of the image, the islands are marked in green) - is made of two small islands that cap the main seamount and ring the volcano's caldera. The last known eruption from the volcano was in 1988 - over twenty years ago - so this is exciting to see a new event. However, the 1988 eruption was apparently quite small (VEI 0), so the last major eruption might have been as far back as 1937 (VEI 2). Beyond that, not much is know about this volcano in the Tongan arc.

The Big Island of Hawaii has it's own undersea mount, Lo'ihi, which in 1996, was rocked by the first ever directly observed eruption of an active underwater volcano in Hawaii.

The eruption was preceded by a swarm of 4,070 earthquakes, the largest of any Hawaiian volcanic eruptions. A total of 4 to 5 square miles of the summit was altered; one section, Pele's Vents, collapsed entirely upon itself, and formed the renamed Pele's Pit.

Aerial: Aerial photos here: New Tonga Eruption

Satellite: Satellite view: View of Tonga eruption from Space 

UPDATE 3-20-09: 'No living thing left' as Tonga volcano erupts: It continued to spew Friday even as a major earthquake with a magnitude of 7.9 rocked Tonga's main island of Tongatapu. "The island itself is totally destroyed, there is no living thing left there, it's all covered in black ash. There are only black stumps where the coconut trees were," he added. "We saw dead birds and fish in the water."


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