September 05, 2008

Crystals Improve Understanding Of Volcanic Eruption Triggers


ScienceDaily (Sep. 1, 2008) — Scientists have exploited crystals from lavas to unravel the records of volcanic eruptions.

The team, from Durham University and the University of Leeds, studied crystal formation from a volcano, in Santorini, in Greece, to calculate the timescale between the trigger of volcanic activity and the volcano's eruption.

They say the technique can be applied to other volcanoes – such as Vesuvius, near Naples, in Italy – and will help inform the decisions of civil defence agencies.

Worldwide, it is estimated that between 50 and 70 volcanoes erupt each year, but due to the long gaps between eruptions at most volcanoes it is hard to understand how any individual volcano behaves. This work allows scientists to better understand this behaviour.

The research, funded by the Natural Environment Research Council (NERC), was recently published in the journal Science.

The scientists looked at crystals from the 1925-28 eruption of Nea Kameni, in Santorini.

Lead author Dr Victoria Martin, of Durham University, showed that the crystal rims reacted with molten rock, or magma, as it moved into the volcano's shallow chamber prior to eruption. This process is thought to be associated with shallow level earthquake activity, as shown by modern volcano monitoring.

By studying the area between the crystal core and the rim the team then worked out how long the rims had existed – revealing how long the magma was in the shallow chamber before it erupted.

The crystals showed the 1925-28 eruption at Nea Kameni took place three to ten weeks after the magma entered the shallow system.

As magma movement typically causes seismic activity, if any future seismic or inflation activity at Nea Kameni can be linked to magma recharge of the volcano, the scientists predict an eruption could follow within a similar timescale.

They hope this method can be applied to other volcanoes, allowing the pre-eruption behaviour to be better understood - and understanding of volcanoes to be extended back further in time.

Co-author Dr Dan Morgan, from the School of Earth and Environment, at the University of Leeds, said: "We hope to develop these techniques further and apply them to more volcanoes worldwide.

"Potentially, these techniques could extend our knowledge of volcanic recharge considerably, as they can be applied to material erupted before volcanic monitoring was commonplace."

Professor Jon Davidson, Chair of Earth Sciences at Durham University, said: "We hope that what we find in the crystals in terms of timescales can be linked with phenomena such as earthquakes.

"If we can relate the timescales we measure to such events we may be able to say when we could expect a volcano to erupt.

"This is an exciting new method that will help us understand the timescales of fundamental volcanic processes driving eruptions."

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ScienceDaily (Aug. 28, 2008) — The geysers of Yellowstone National Park owe their existence to the "Yellowstone hotspot"--a region of molten rock buried deep beneath Yellowstone, geologists have found.

But how hot is this "hotspot," and what's causing it?

In an effort to find out, Derek Schutt of Colorado State University and Ken Dueker of the University of Wyoming took the hotspot's temperature.

The scientists published results of their research, funded by the National Science Foundation (NSF)'s division of earth sciences, in the August, 2008, issue of the journal Geology.

"Yellowstone is located atop of one of the few large volcanic hotspots on Earth," said Schutt. "But though the hot material is a volcanic plume, it's cooler than others of its kind, such as one in Hawaii."

When a supervolcano last erupted at this spot more than 600,000 years ago, its plume covered half of today's United States with volcanic ash. Details of the cause of the Yellowstone supervolcano's periodic eruptions through history are still unknown.

Thanks to new seismometers in the Yellowstone area, however, scientists are obtaining new data on the hotspot.

Past research found that in rocks far beneath southern Idaho and northwestern Wyoming, seismic energy from distant earthquakes slows down considerably.

Using the recently deployed seismometers, Schutt and Dueker modeled the effects of temperature and other processes that affect the speed at which seismic energy travels. They then used these models to make an estimate of the Yellowstone hotspot's temperature.

They found that the hotspot is "only" 50 to 200 degrees Celsius hotter than its surroundings.

"Although Yellowstone sits above a plume of hot material coming up from deep with the Earth, it's a remarkably 'lukewarm' plume," said Schutt, comparing Yellowstone to other plumes.

Although the Yellowstone volcano's continued existence is likely due to the upwelling of this hot plume, the plume may have become disconnected from its heat source in Earth's core.

"Disconnected, however, does not mean extinct," said Schutt. "It would be a mistake to write off Yellowstone as a 'dead' volcano. A hot plume, even a slightly cooler one, is still hot."

The Mystery of Global Warming's Missing Heat


Some 3,000 scientific robots that are plying the ocean have sent home a puzzling message. These diving instruments suggest that the oceans have not warmed up at all over the past four or five years. That could mean global warming has taken a breather. Or it could mean scientists aren't quite understanding what their robots are telling them.

This is puzzling in part because here on the surface of the Earth, the years since 2003 have been some of the hottest on record. But Josh Willis at NASA's Jet Propulsion Laboratory says the oceans are what really matter when it comes to global warming.

In fact, 80 percent to 90 percent of global warming involves heating up ocean waters. They hold much more heat than the atmosphere can. So Willis has been studying the ocean with a fleet of robotic instruments called the Argo system. The buoys can dive 3,000 feet down and measure ocean temperature. Since the system was fully deployed in 2003, it has recorded no warming of the global oceans.

"There has been a very slight cooling, but not anything really significant," Willis says. So the buildup of heat on Earth may be on a brief hiatus. "Global warming doesn't mean every year will be warmer than the last. And it may be that we are in a period of less rapid warming."

In recent years, heat has actually been flowing out of the ocean and into the air. This is a feature of the weather phenomenon known as El Nino. So it is indeed possible the air has warmed but the ocean has not. But it's also possible that something more mysterious is going on.

That becomes clear when you consider what's happening to global sea level. Sea level rises when the oceans get warm because warmer water expands. This accounts for about half of global sea level rise. So with the oceans not warming, you would expect to see less sea level rise. Instead, sea level has risen about half an inch in the past four years. That's a lot.

Willis says some of this water is apparently coming from a recent increase in the melting rate of glaciers in Greenland and Antarctica.

"But in fact there's a little bit of a mystery. We can't account for all of the sea level increase we've seen over the last three or four years," he says.

One possibility is that the sea has, in fact, warmed and expanded — and scientists are somehow misinterpreting the data from the diving buoys.

But if the aquatic robots are actually telling the right story, that raises a new question: Where is the extra heat all going?

Kevin Trenberth at the National Center for Atmospheric Research says it's probably going back out into space. The Earth has a number of natural thermostats, including clouds, which can either trap heat and turn up the temperature, or reflect sunlight and help cool the planet.

That can't be directly measured at the moment, however.

"Unfortunately, we don't have adequate tracking of clouds to determine exactly what role they've been playing during this period," Trenberth says.

It's also possible that some of the heat has gone even deeper into the ocean, he says. Or it's possible that scientists need to correct for some other feature of the planet they don't know about. It's an exciting time, though, with all this new data about global sea temperature, sea level and other features of climate.

"I suspect that we'll able to put this together with a little bit more perspective and further analysis," Trenberth says. "But what this does is highlight some of the issues and send people back to the drawing board."

Trenberth and Willis agree that a few mild years have no effect on the long-term trend of global warming. But they say there are still things to learn about how our planet copes with the heat.