WATCHING THE PLUMES

By Pam Eastlick

Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.

Having done animals and medicine for a while, it’s time to turn to Mother Earth and see what the latest news is about her periodic eruptions. Our first story concerns a volcano we’ve discussed several times here in this column. It’s not your typical volcano, but there’s no denying that it’s been destructive. But what makes Lusi really unique is the possibility that we humans really have become a geologic force.

LAYING THE BLAME

Researchers have discovered new data that provides the strongest evidence so far that Lusi, the world’s biggest mud volcano, which killed 13 people in 2006 and displaced thirty thousand people in East Java, Indonesia, was not caused by an earthquake.

There have been conflicting claims about Lusi’s origins. Lapindo Brantas, a large Indonesian drilling firm was drilling a gas exploration well near where Luisi erupted and many people think that drilling was the trigger for the volcano. But Lapindo Brantas has claimed that an earthquake that occurred 280 kilometers (174 miles) away was what caused the volcano to erupt. They backed up their claims in an article accepted for publication in the journal Marine and Petroleum Geology, by lead author Nurrochmat Sawolo, senior drilling adviser for Lapindo Brantas, and colleagues.

In response, a group of scientists from the United Kingdom, United States, Australia and Indonesia led by Richard Davies, director of the Durham Energy Institute, have written a discussion paper in which they refute the main arguments made by Nurrochmat Sawolo and document new data that provides the strongest evidence to date of a link between the well and the volcano. That paper has been accepted for publication in the same journal.

"The disaster was caused by pulling the drill string and drill bit out of the hole while the hole was unstable," Davies said. "This triggered a very large ‘kick’ in the well, where there is a large influx of water and gas from surrounding rock formations that could not be controlled.

"We found that one of the on-site daily drilling reports states that Lapindo Brantas pumped heavy drilling mud into the well to try to stop the mud volcano. This was partially successful and the eruption of the mud volcano slowed down. The fact that the eruption slowed provides the first conclusive evidence that the bore hole was connected to the volcano at the time of eruption."

Lusi first erupted on 29 May 2006, near Indonesia’s second largest city of Surabaya. The mud from the volcano now covers nearly three square miles and is 65 feet thick. It has destroyed four villages and 25 factories. Thirteen people died as a result of a rupture in a natural gas pipeline underneath one of the holding dams. The Lusi crater has been oozing enough mud to fill 50 Olympic size swimming pools every day. All efforts to stem the mud flow have failed, including the construction of dams, levees, drainage channels, and even plugging the crater with concrete balls. Lusi may continue to erupt for decades, scientists believe.

Arguments over what caused the volcano to erupt have stalled the establishment of liability for the disaster and delayed compensation to thousands of people affected by the mud. The Yogyakarta earthquake that occurred at the time of the volcano was cited by some as a possible cause of the eruption, but the research team rejected this explanation.

View of the Lusi mud volcano crater and the dikes and dams constructed to contain the still-oozing mud. (Credit: Courtesy of Channel 9 Australia)

Richard Davies may in fact be right that Lapindo Brantas caused the eruption with their drilling. But the real fun is going to be to get them to admit it. Just like the volcano isn’t done spewing its mud over everyone, I doubt that the mud-slinging of blame is over either!

Now we’ll turn our attention to another volcano in our area of the world. But there’s no question that people had nothing to do with this one. It’s been around for longer than there have been people and it not only has deep roots in time, it has them in the earth too. Read on!

MAKING HAWAII

Ever since the 60’s when geologists began to realize that Alfred Wegner was right with his wacko theories about cruising continents, the island of Hawaii has presented a bit of a problem. We could readily explain volcanoes at the boundaries where plates split apart or collide, the island of Hawaii was bang in the middle of a plate but there was no denying that it was in fact, a giant volcano.

A classic explanation, proposed nearly 40 years ago, has been that magma is supplied to these volcanoes from upwellings of hot rock, called mantle "plumes," that originate deep in the Earth’s mantle. It’s a nice theory, but substantiation proved a little hard to provide. Now, a sophisticated array of seismometers deployed on the sea floor around Hawaii has provided the first high-resolution seismic images of a mantle plume with its origins at least 1,000 miles below the Earth’s surface.

This unprecedented glimpse of the roots of the Hawaiian "hot spot" is the product of an ambitious project known as PLUME, for Plume-Lithosphere Undersea Melt Experiment, which collected and analyzed two years of data from sea floor and land-based seismometers.

The PLUME images show a seismic anomaly beneath the island of Hawaii, the chain’s largest and most volcanically active island. Critics of the plume model have argued that the magma in hot spot volcanoes comes from relatively shallow depths in the upper mantle not deep plumes, but the anomaly observed by the PLUME researchers goes down at least 1,000 miles . Rock within the anomaly is also calculated to be significantly hotter than its surroundings, as predicted by the plume model.

Erik Hauri, also of Carnegie’s Department of Terrestrial Magnetism, led the geochemical component of the research. "We had suspected from geochemistry that the center of the plume would be beneath the main island, and that turns out to be about where the hot spot is centered," he says. "We also predicted that its width would be comparable to the size of island of Hawaii and that also turned out to be true. But those predictions were merely theoretical. Now, for the first time, we can really see the plume conduit."

Location of seismic velocity anomaly at a depth of 746 miles beneath Hawaiian Islands (outlines). Orange color indicates low S-wave velocities, implying higher rock temperatures. Open boxes show locations of sea-floor seismometers. (Credit: Image courtesy of Science)

Lucky for the people of Indonesia that the plume under Lusi isn’t that big (or that hot!). And now a look using the same techniques at a supervolcano; one that most people who visit it aren’t even aware of.

THE BIGGEST ONE?

Yellowstone National Park is one of the premier vacation destinations in the United States. All those boiling hot calderas and geysers were a fascinating find in the middle of uncharted wilderness 200 years ago and they continue to fascinate today. But if you think that their existence is a mystery to the layman, it was also a mystery to geologists. What was all that activity doing in the middle of a continent?

At the same time geologists were wondering about Hawaii, they began to realize with dawning interest (and some horror) that the two questions had the same answer. Not only was there a gigantic mantle plume under Hawaii, there was also one under Wyoming and Yellowstone National Park isn’t just an interesting destination for tourists, it’s the mouth of one of the world’s largest volcanoes.

Using the same techniques as the researchers in Hawaii (although this group didn’t have to contend with the problem of how to get your seismometers on the ocean floor!) a team from the University of Utah has published a picture of the plumbing that feeds the Yellowstone supervolcano which shows a plume of molten rock that stars at least 400 miles down and rises at an angle from the northwest. This contradicts claims that there is no deep plume under Yellowstone, only shallow hot rock moving like slowly boiling soup.

A related study used gravity measurements to indicate the banana-shaped magma chamber of hot and molten rock a few miles beneath Yellowstone is 20 percent larger than previously believed, so a future cataclysmic eruption could be even larger than thought.

Some 17 million years ago, the Yellowstone hotspot was located beneath the Oregon-Idaho-Nevada border region, feeding a plume of hot and molten rock that produced "caldera" eruptions — the biggest kind of volcanic eruption on Earth.

As North America slid southwest over the hotspot, the plume generated more than 140 huge eruptions that produced a chain of giant craters — calderas — extending from the Oregon-Idaho-Nevada border northeast to the current site of Yellowstone National Park, where huge caldera eruptions happened 2.05 million, 1.3 million and 642,000 years ago.

These eruptions were 2,500, 280 and 1,000 times bigger, respectively, than the 1980 eruption of Mount St. Helens. The eruptions covered as much as half the continental United States with inches to feet of volcanic ash. The Yellowstone caldera, 40 miles by 25 miles, is the remnant of that last giant eruption.

The Yellowstone caldera, like other calderas on Earth, huffs upward and puffs downward repeatedly over the ages, usually without erupting. Since 2004, the caldera floor has risen 3 inches per year, suggesting recharge of the magma body beneath it.

Scientists have debated for years whether Yellowstone’s volcanism is fed by a plume rising from deep in the Earth or by shallow churning in the upper mantle caused by movements of the overlying crust. The current study has produced the most detailed image of the Yellowstone plume yet published.

But a preliminary study by other researchers suggests Yellowstone’s plume goes deeper than 410 miles, ballooning below that depth into a wider zone of hot rock that extends at least 620 miles deep.

Seismic imaging was used by University of Utah scientists to construct this 3-D picture of the Yellowstone hotspot plume of hot and molten rock that feeds the shallower magma chamber (not shown) beneath Yellowstone National Park, outlined in green at the surface, or top of the illustration. (Credit: University of Utah)

Researchers say that if the Yellowstone supervolcano were to erupt, it would devastate the entire United States. Just more proof that Mother Nature may just be the biggest mother of them all!