Tag Archives: hotspot

Huge underwater eruption created giant volcano off the coast of Africa

The beautiful island of Mayotte was shaken by numerous volcanic temblors. Image credits: Yane Mainard.

Volcanic shake

About half a year ago, seismologists noticed something unusual off the coast of Mayotte, an overseas French territory between Africa’s eastern coast and Madagascar. Sensors all around the world picked up seismic waves coming from around the island, but the source was largely unknown.

The locals felt it too. Almost every day, they felt small rumbles, stressing out about what the source might be, and authorities had little answers. French researchers had a hunch what the source might be, but without an on-site expedition, it was impossible to confirm. In February, such an expedition was launched. Nathalie Feuillet of the Institute of Geophysics in Paris (IPGP) and colleagues installed six seismometers on the seafloor, 3.5 kilometers beneath the surface, to monitor the seismic activity.

They pinpointed the seismic area, triangulating a region some 20-50 km deep — but this was only the first step. After the area was identified, researchers mapped it using sonar, finding evidence of a tall volcanic mountain formed underwater, and a huge quantity of solidified lava around it.

The outline of the volcano (in red) was excellently outlined by the sonar beams. The 800-meter (half a mile) volcano was built from nothing in just six months. The eruption was so dramatic that the island of Mayotte sank by about 13 centimeters (5 inches) and moved eastwards about 10 centimeters (4 inches). The sonar also revealed 5 cubic km (1.2 cubic miles) of magma on the seafloor Image credits: MAYOBS TEAM (CNRS/IPGP-UNIVERSITÉ DE PARIS/IFREMER/BRGM).

Competing theories

Mayotte is part of the Comoros archipelago, an archipelago formed through volcanic eruptions. However, although some areas of the Comoros are still very active, the last eruption around Mayotte took place about 7,000 years ago. It’s not just the location of this new volcano that’s a bit puzzling, its nature is also a mystery.

There are several competing theories regarding the nature of this volcanic range. Most volcanoes are found along mid-ocean ridges — underwater mountain ranges formed where the Earth’s tectonic plates are pulling apart, and where convection currents from the mantle are bringing magma closer to the surface. However, this isn’t really the case in the Comoros.

Another possibility is that of a hotspot. A volcanic hotspot is an area where a rising mantle plume comes really close to the surface, producing volcanic activity. The classic example is Hawaii, although the nearby island of Reunion was also formed this way. Hot spots aren’t affected by plate tectonics, and they stay in place while tectonic plates move about, typically leaving a “trail” of volcanoes on the surface. This is consistent with the fairly deep earthquakes observed around Mayotte, which would also suggest that the volcanic magma chamber is also very deep. But the evidence isn’t convincing enough to definitively say that there’s a hotspot there.

Depiction of a rift breaking down into multiple rigid blocks. Image credits: Italian Institute for Geosciences.

Another likely culprit is the geological process of rifting. East Africa is one of the world’s most active rift zones, with the African tectonic plate splitting into two separate plates. The rifting area isn’t exactly close to Mayotte, but rifting tends to break large areas into rigid blocks, and this might be responsible for the volcanic events.

Most intriguingly, it could be a combination of some (or all) of the above, making Mayotte one of the most exciting volcanic areas to study.

As for the island’s inhabitants, they still have reason to worry. The volcano is probably too deep to threaten the island in any way — the eruptions are too deep to affect the surface and even a potential collapse of one of its flanks would likely be too deep to generate a tsunami. However, the earthquakes seem to be slowly migrating towards the island, which could potentially lead to a collapse of the island’s flank itself — which would, of course, be much more dangerous. Given this turn of events, Feuillet wants to extend the mission for a few months and get a much better view of what’s happening with this volcanic activity in order to assess the potential risk to the locals. After this is done, results will also be published in a journal, Feuillet says.

Scientists find the world’s largest volcanic hotspot track

Scientists have discovered the longest chain of continental volcanoes in the world, stretching almost 2000 km (1200 miles) on Australia’s coast. The volcanic track includes 15 volcanoes formed over 30 million years ago.

Image credits: Drew Whitehouse/NCI National Facility

Volcanoes come in various shapes and sizes. There’s stratovolcanoes, cinder cones, shield volcanoes… and then there’s hotspots. In geology, a hotspot is a volcanic region in which the underlying mantle is considerably hotter than the surrounding mantle, and starts feeding a volcano; we’re talking about mantle plumes up to 3000 km (1800 miles) deep. Notable examples are Yellowstone and Hawaii.

The thing is that the tectonic plates are not immobile – they move; granted, they move a few centimeters per year, but in millions of years, they can cross huge distances. However, the hotspot doesn’t move, it remains in the same place, and as the plates move above it, they create a trail of volcanoes. Such is the case with the newly discovered Cosgrove hotspot track.

It consists of 15 ancient volcanoes that researchers already knew about, but didn’t know they were created by the same hotspot.

“We realised that the same hotspot had caused volcanoes in the Whitsundays and the central Victoria region, and also some rare features in New South Wales, roughly halfway between them,” lead researcher Rhodri Davies from the Australian National University said in a press release. “The track is nearly three times the length of the famous Yellowstone hotspot track on the North American continent.”

It’s normal not to think the volcanoes are connected in any way – after all, they’re separated by more than 700 km (400 miles), but they all have the same chemical signature, with the southern volcanoes being younger than the northern ones. But the question arises, if the plate moved continuously, why is the distance between the volcanoes so big? Shouldn’t there be many other volcanoes, like with the other hotspots?

Over millions of years, the Pacific Plate has moved over the Hawaii hotspot, creating a trail of underwater mountains that stretch across the Pacific. Image via Wikipedia.

Well, researchers found that some areas of the Australian continent are too thick to let the heat of the mantle rise up and create a volcano. This might actually provide valuable information into how hotspots are formed and how the magma can breach through to the surface. Researchers have also projected where the hotspot is now, at the current rate of movement of the Australian plate, 7 cm per year.

“There is some seismicity in this region, there’s been some earthquakes around that location recently which does hint that something is going on there, but we haven’t been able to find any seamounts or volcanic regions at present,” Davies told Stuart Gary over at the ABC.

Swarm of earthquakes shake Yellowstone National Park

Could the Yellowstone supervolcano be waking up?

faithful

In his 53 years of monitoring seismic activity in and around the Yellowstone Caldera, Bob Smith has never witnessed two simultaneous earthquake swarms; now, the Utah University geophysicist has seen not two, but three such swarms.

“It’s very remarkable,” Smith said. “How does one swarm relate to another? Can one swarm trigger another and vice versa?”

Because such an event is unprecedented, Smith doesn’t want to jump to conclusions, and doesn’t think this is a signal of any potential volcanic eruption.

“A total of 130 earthquakes of magnitude 0.6 to 3.6 have occurred in these three areas, however, most have occurred in the Lower Geyser Basin,” a University of Utah statement said. “Notably much of seismicity in Yellowstone occurs as swarms.”

No significant changes are to be expected, except possibly for geyser activity.

“We know that a significant enough earthquake in the region has potential to alter geyser activity,” the spokesman said. “A strong enough earthquake, like the one that occurred out at Hebgen Lake in 1959, did change the interval of Old Faithful eruptions.”

Undersea volcano about to create new Canary Island

It’s only so often that you get to see geology in the making, and this is a remarkable event indeed. Volcanologists studying an undersea volcano erupting near the island of El Hierro announced that the volcano, which is located at just 70 meters below sea level, will probably create a new island.

The Canarian hot spot

Over the past couple of weeks, volcanic activity off the Canary islands has caused jets of water to rise even some 20 meters above sea level, and locals claim to have seen rocks being thrown out of the water as well. After science stepped in, it was revealed that the water in the area was significantly warmer than surrounding sea, and the culprit was, as expected, what is called the Canarian hotspot.

Hotspots are remarkable volcanic regions where the mantle is much hotter than normal, and closer to the surface than usual. Aside from this region, other remarkable examples are the Hawaiian islands and the Yellowstone volcano.

Shaking things up

Since July 2011, over 10.000 small earthquakes shook the island of El Hierro; however, since October, they have become more powerful (though not very dangerous), at over 4 degrees on the Richter scale. The main problem was caused by the supherous gases that were released by these temblors.

However, an interesting phenomena occurred: the earthquakes moved towards to the north, and rose upwards, closer to the surface. However, at the moment, there is no imminent danger of eruption, so residents of El Hierro have already started thinking up names for the new territory.

Via Wired