美國火山活動20110812

Surprise Underwater Volcanic Eruption Discovered

An undersea volcano has erupted off the coast of Oregon, spewing forth a layer of lava more than 12 feet (4 meters) thick in some places, and opening up deep vents that belch forth a cloudy stew of hot water and microbes from deep inside the Earth.

Scientists uncovered evidence of the early April eruption on a routine expedition in late July to the Axial Seamount, an underwater volcano that stands 250 miles (400 kilometers) off the Oregon coast.

The discovery came as a surprise, as researchers attempted to recover instruments they'd left behind to monitor the peak a year earlier. When the researchers hefted a seafaring robotic vehicle overboard to fetch the instruments, the feed from the onboard camera sent back images of an alien seafloor landscape.

"At first we were really confused, and thought we were in the wrong place," said Bill Chadwick, a geologist with Oregon State University. "Finally we figured out we were in the right place but the whole seafloor had changed, and that's why we couldn't recognize anything. All of a sudden it hit us that, wow, there had been an eruption. So it was very exciting."

In addition to producing hardened lakes of blobby lava, in places more than a mile (1.6 km) across, the eruption changed the architecture of the region's seafloor hot springs.

"There are more vents, they're higher temperature, and there are microbes living in them that are usually deep in the crust that come up to the surface in these events," Chadwick told OurAmazingPlanet.

Eruption predicted

The Axial Volcano rises 3,000 feet (900 m) above the seafloor, the most active of a string of volcanoes along the Juan de Fuca Ridge, a plate boundary where the seafloor is slowly pulling apart.

Chadwick and colleagues have been keeping tabs on the peak since it last erupted in 1998. Thanks to a monitoring system they developed to measure the mountain's minute movements, the team predicted the volcano was due for another eruption sometime between 2011 and 2014.

"So for me, it's a very exciting thing that this worked!" Chadwick said.

The instruments kept track of the movement of the seafloor, which very gradually inflates and deflates like a giant, magma-filled balloon, Chadwick said, collapsing suddenly after an eruption, and rising, in this case, by about 6 inches (15 cm) per year in the lead up to an eruption.

First long-term picture

Scientists have long known about the existence of subsea volcanoes, but information on their behavior is relatively sparse. Eruptions were first observed in the 1990s, and, although technology has improved, getting to the underwater peaks to study them is difficult.

Data from the Axial Seamount's recent eruption will provide the first long-term picture of a subsea volcano from one eruption to the next. [Infographic: Tallest Mountain to Deepest Ocean Trench]

Chadwick said scientists are still trying to figure out how seafloor volcanoes differ from their terrestrial counterparts.

It could be it's easier to predict ocean eruptions, Chadwick said. It's possible that because the crust is thinner there, and magma is in ready supply, the mountains' slow inflations provide a good analogue for knowing when eruptions will occur. However, he cautioned that a single successful prediction wasn’t enough to forecast what the future holds.

"At Axial we've only seen this once, so we don't know for sure it's going to be reliable," Chadwick said. "So we'll certainly keep making these measurements, and hopefully be around to see what happens next."

Alaskan volcano showing signs it will erupt

 ANCHORAGE, Alaska — Recent satellite images of a remote Alaska volcano along a flight route for major airlines show it may be poised for its first big eruption in 10 years, scientists said.

The Alaska Volcano Observatory has issued an eruption advisory for the 5,676 foot-tall Cleveland Volcano, located on the uninhabited island of Chuginadak in the Aleutian chain about 940 miles southwest of Anchorage.
The advisory was based on "thermal anomalies" detected by satellite, the observatory said on Thursday. Those measurements indicate the volcano could erupt at any moment, spewing ash clouds up to 20,000 feet above sea level with little further warning, the observatory said.
A major eruption could disrupt international air travel because the Cleveland Volcano, like others in the Aleutians, lies directly below the commercial airline flight path between North America and Asia, said John Power, scientist-in-charge at the Alaska Volcano Observatory.
The volcano's last major eruption came in 2001, when it blasted ash more than 5 miles into the sky and spilled lava from the summit crater. Cleveland has experienced several smaller eruptions or suspected eruptions since then.
So far, airlines have not changed their flight patterns because of Cleveland's heat emissions, said Steve McNutt, a University of Alaska Fairbanks scientist who works at the observatory.


Scientists are not always certain about what is happening at the remote volcano, observatory officials said. The town of Nikolski, the nearest settlement to the Cleveland Volcano, is 45 miles away.

Although Cleveland is among the most active of Alaska's roughly 90 volcanoes, no seismic equipment is set up there because the costs of working in such a remote area are prohibitive, observatory officials said.
Still, Cleveland is the only Alaska volcano blamed for an eruption-caused human death in recorded history. A U.S. soldier who was stationed on Chuginadak Island during World War Two disappeared during an eruption and was presumed killed.
Without sophisticated monitors like those used to keep tabs on volcanoes closer to Anchorage and other populated areas, scientists must rely on a variety of other observations to track Cleveland's eruptions, McNutt said. Those include satellite data, eyewitness reports and video from mariners and pilots in the area.
"Cleveland is a particular bugaboo for us because it is right on the air route" with no seismic equipment, Power said.

評論:

自從年初2月的X級太陽耀斑之後，地球上的地震和火山活動就有明顯的增加；在8月9日又發生了X6.9極的太陽耀斑，整個地球的火山活動也似乎更蠢蠢欲動。

美國北部阿拉斯加已經被證實有大量的火山活動，有煙不斷的從火山口冒出，令人開始擔憂他的爆發期應該不遠了。

美國的西部海底也已經被證實了有很多海底火山的活動，岩漿也已經噴發將近4公尺。至於在美國西岸的陸地上，從今年4月以來在許多不同的區域，都被發現不斷的有煙從疑似火山口處噴出。美國的火山似乎也蠢蠢欲動了。