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Geophenomena

New addition to the Aleutian family
Yellowstone geysers heat up
First dead zone forecast

New addition to the Aleutian family

While searching for deep-sea corals on the ocean floor near the Aleutian Islands, researchers instead found Alaska’s first known active underwater volcano.

A biological expedition run by NOAA’s National Marine Fisheries Service first sighted the infant cone in June 2002. Not until June of this year did a team led by Jennifer Reynolds, a marine geologist at University of Alaska Fairbanks, map the structure in detail using multi-beam sonar.

Multibeam sonar data provide a map of the Alaskan seafloor and a new-found submarine volcano (upper left), surrounded by a field of lava flows. Image courtesy Jennifer Reynolds.


They discovered a peak 580 meters (1,903 feet) tall with a 4-kilometer-wide base (one-third to one-half the height of nearby on-land volcanoes), as well as a volcanic lava field extending over 14 kilometers. As part of an island arc formed by a subduction zone, this young volcano is probably prone to explosive eruptive events — which means it poses a potential threat to passing vessels because of its proximity to the ocean’s surface, only 115 meters (377 feet) below sea level.

The Alaska Volcano Observatory already has plans to put a seismic monitor on a nearby island by 2005. Reynolds will join an expedition next summer to look more carefully at the newfound volcano. “We really know just a little bit about this volcano,” Reynolds says. Though it apparently was active within the past millennium, she says, “we don’t know whether that means 50 years ago or 800 years ago.”

Naomi Lubick

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Yellowstone geysers heat up

Since July 23, some trails within the Norris Geyser Basin in northern Yellowstone National Park have been closed to visitors due to high ground temperatures and increased thermal activity that could affect visitor and employee safety. To identify the sources and explain the increased activity, and to gauge any risks of seismic activity or hydrothermal explosions, geologists are fitting the Back Basin at Norris with a series of new instruments, making it the most heavily monitored geyser basin in the world.

The increased thermal activity includes the formation of new mud pots, greater turbidity of thermal pools, increased steam discharge, and changes in geyser eruption intervals and output. Ground temperatures can reach up to 100 degrees Fahrenheit above normal, and vegetation dies from the high temperatures.

Geysers and thermal waters in Yellowstone National Park, where geologists have fitted the Back Basin at Norris Geyser with instruments to observe increased thermal activity. Photo by Bruce Molnia, Terra Photographics.

In August, scientists with the Yellowstone Volcano Observatory (YVO) responded to these dramatic changes by equipping the basin with a network of seismographs, GPS receivers and thermometers. YVO is an instrument-based monitoring facility run by the U.S. Geological Survey (USGS), the University of Utah and the National Park Service.

“Never before has a geyser basin been observed in this way,” says Jacob Lowenstern, the USGS lead scientist at Yellowstone Volcano Observatory. “We want to look at the geophysical and thermal data and to understand the day-to-day activities in the geyser basin.”

The GPS sensors will detect any small movements or ground deformation. Seven new broadband seismometers will detect long-period seismic activity, such as vibrations due to water or gas movement through underground cracks or deeper volcanic sources. Thermometers will continuously document pulses of water out of individual pools, which may be tied to signals measured by the GPS receivers and seismometers. The Integrated Research Institutes in Seismology and the University NAVSTAR Consortium are also helping to provide equipment and technical support.

In addition to observing the daily activity of geyser basins, scientists are also hoping to detect any precursory activity should a hydrothermal explosion occur. Hydrothermal explosions are fairly common in the park, occurring roughly once per year; however, they tend to be small and usually go unwitnessed. Therefore, geologists know little about predicting them. “If anything does occur in this case, it will be a great opportunity to learn about what precedes the explosions,” Lowenstern says.

Yellowstone is a dynamic environment. Each summer, there is a noticeable increase in the steam discharge and a change in color of many geysers and thermal pools in the Norris Geyser Basin that is apparently related to the increased emission of deep, hot waters. But this year, that annual disturbance is larger than normal. Lowenstern says, “there is lots of new activity, and steam is finding its way to the surface in places it never has.”

Still, scientists at the observatory caution that the increased activity doesn’t necessarily indicate a greater probability of an impending hydrothermal explosion. The last large hydrothermal explosion at Norris was the Porkchop Geyser explosion in 1989, which tossed meter-sized boulders into the air. Porkchop remained silent until this past July, when it began erupting water again.

Norris’ Back Basin will remain closed to the public as long as ground temperatures and steam vents remain a risk. As of Aug. 15, researchers planned to keep the monitoring instruments in place until the trails reopen — at least a month — to allow the scientists time to study the data and to learn more about hydrothermal activities.

Megan Sever

Links:

Yellowstone Volcano Observatory
Yellowstone National Park

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First dead zone forecast

Each summer, an oxygen-depleted area up to twice the size of the Chesapeake Bay forms on the continental shelf in the Gulf of Mexico — wreaking havoc on the Gulf fishing industry. The size varies from year to year, only revealing its extent during the event itself. Now, oceanographers have developed a model that, for the first time, predicts the size of this so-called dead zone off the coasts of Texas and Louisiana. The model couples nutrient and discharge data recorded in the Mississippi and Atchafalaya rivers during the spring with an advection factor that accounts for variable Gulf currents to predict the eventual size of the oxygen-depleted area.

Chlorophyll-a is a proxy for phytoplankton biomass. This 2003 image shows the pattern of chlorophyll and biomass in late spring, just prior to the appearance of the dead zone. The area of high biomass is typical for this time of year. The smaller size of the dead zone in 2003 is likely due to tropical storms and not changes in nutrient input or total biomass. Satellite image courtesy of NOAA.

“The combination of the nutrient load and the advection term explains 88 percent of the year-to-year variation,” says Don Scavia, the chief scientist of NOAA’s National Ocean Service.

Along with researchers from the Louisiana Universities Marine Consortium and Louisiana State University, Scavia also reports in the May Limnology and Oceanography that the model shows the phenomenon is relatively recent and that efforts to stem it may prove more difficult than previously thought.

However, the successful modeling of the dead zone’s range shows that researchers have a solid understanding of the science that underlies the event. “It gives us a little more confidence that we know how it is working — what makes it form and dissipate every year,” says co-author Gene Turner, a biological oceanographer at Louisiana State University.

The dead zone begins to form in spring and early summer when meltwater joins nutrient-laden runoff from the agriculturally dominated watershed. When it flows into the colder, saltier Gulf, this less dense water forms a surface layer where, with abundant nutrients, algae flourish. “It’s like pea soup out there,” Turner says. When the algae die and sink, oxygen-consuming decay begins and any bottom-dwelling organisms that can’t escape the vast area die (hence the name, dead zone). The cycle continues until temperatures cool and winds pick up in the fall, allowing the layers to mix; tropical storms and hurricanes could mix the layers earlier.

Understanding how nutrient loads affect this cycle is essential to policy decisions being made about future land use in the watershed. The Mississippi River drains 41 percent of the contiguous United States, an area with abundant fertilizer inputs. Land-use changes in the watershed over the last 50 years have nearly tripled the amount of nitrogen delivered to the Gulf. More than half the estuaries in the United States are now faced with the problem of coastal eutrophication.

Although oxygen depletion, known as hypoxia, has been forming on the Gulf shelf for more than three decades, researchers only began to systematically monitor it in 1985. But using historic river nutrient data, Scavia’s team was able to use the model to “hindcast” the size of hypoxic events going back to 1968.

“The model confirms that the hypoxia was not very large, if present, decades ago,” Turner says. “So that just reassures us again that this is a man-made phenomenon. It’s not something that’s natural.”

According to the model, between 1985 and 1992, the hypoxic region averaged 8,300 square kilometers. Between 1993 and 2001 it rose to an average of 16,000 square kilometers. The new model may help efforts to reduce that figure to less than 5,000 square kilometers by 2015, a goal set forth by the 2001 Mississippi River/Gulf of Mexico Watershed Nutrient Task Force. Achieving that goal will likely require a 30 percent reduction in nutrient loading. Model scenarios, however, suggest that loads may need to be reduced by up to 45 percent to meet the target in some years.

“We’re just offering a caution,” Turner stresses. “The model is good to a certain level of prediction, but there may be other things that happen. For example, climate change may alter the discharge of the river.”

Although the model successfully explains a lot of the variability in the size of the zone from year to year, what it cannot predict is severe weather. In late June and early July of this year, two storms — Tropical Storm Bill and Hurricane Claudette — swept through the Gulf, disrupting the stratification. A monitoring cruise in late July found the dead zone to be 8,560 square kilometers, about 6,000 square kilometers less than predicted. However, researchers expect that stratification will return and the zone will enlarge before it finally dissipates in the fall.

Sara Pratt
Geotimes contributing writer


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