Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Ice cores disagree on origin of White River ash deposit


One anticipated component missing from an ice core drilled through a high-mountain, Alaskan ice field may force researchers to rethink the geologic history of that region.

Ohio State University scientists had expected to find a thick layer of volcanic tephra - evidence of a massive historic eruption - near the bottom of core they drilled between Mount Bona and Mount Churchill, both ancient volcanoes, in southeast Alaska’s St. Elias Mountain Range. That tephra layer would provide new evidence that Mount Churchill had been the source of an eruption that blanketed hundreds of thousands of square miles in the Pacific Northwest, creating a deposit known as the White River Ash.

The problem is that the ice core contains no ash layer. “Our drill site was so close to the crater of Mount Churchill that if it had erupted in 803 A.D., then ash would have been preserved somewhere in our record in the core,” explained Tracy Mashiotta, a research associate with the Byrd Polar Research Center. “We drilled all the way through the glacier to the bedrock below and didn’t find any ash.” “Without a visible ash layer in the core, we don’t believe that Mount Churchill could have been the source for that deposit.” explained Lonnie Thompson, professor of geological sciences and researcher with the Byrd Polar Research Center.

They reported their findings today at the meeting of the American Geophysical Union in San Francisco. The researcher’s conviction lies with the analysis of six cores they recovered in 2003 from an ice field in a saddle between the two peaks. Along with five shallow cores ranging from 10.5 meters (34.4 feet) to 114 meters (374 feet), the researchers drilled a complete 460-meter (1,509-foot) core through the ice to bedrock, capturing a climatological record preserved in the ice.

The five shallow cores contain a record ranging from eight to 64 years. The long core - itself the longest ever drilled through a mountainous glacier – dates back nearly 1,500 years. And that presents a problem for the current interpretation of geology in the region. Researchers have dated the two White River Ash deposits to two eruptions in the last two millennia - one in approximately 803 A.D. and the other in around 63 A.D – that were thought to come from the same volcano. And many scientists have suspected Mount Churchill was the site of those eruptions. If so, those blasts would have deposited layers of volcanic ash at the top of the mountain, including on the ice present at the time. And over time, that layer would have been buried deep in the ice.

Expecting to find it, the OSU team had engineered a new drill bit for their drill capable of piercing the expected one-meter-thick (3.2-foot) ash layer. But it wasn’t there. “Both ash deposits have been thought to come from the same volcano,” Mashiotta said. “If we didn’t see evidence from the ice core pointing to an eruption in 803 A.D., it’s unlikely that Mount Churchill was the source of the earlier deposit from 63 A.D.

Besides the missing ash layer, the core offered more evidence that the White River Ash wasn’t born on Mount Churchill. Towards the bottom of the long core, they discovered layers of pebbles trapped in the ice. The pebbles were made of granodiorite, a non-volcanic rock. In fact, granodiorite is widely seen as a marker that shows the passing of the massive ice sheets that once blanketed the Western Cordillera of North America. Thompson said the bottom two meters (6.5 feet) of the core contained numerous layers of these pebbles as well.

The research team serendipitously arrived at a time when the surface at the summit of Mount Churchill - near the crater - was free of snow cover. There they found large granodiorite stones and boulders. Had the mountain erupted since they were deposited, Thompson said, they would have been covered by deep ash. Thompson believes both the stones at the crater rim and the pebble layers are remnants of those ice sheets. And the fact that they found multiple layers in the core suggests the area had been overrun by ice several times.

Another clue was missing from the core that might have pointed to Mount Churchill as the source of the deposit. They found distinct markers of high sulfate content at various points in the core, traceable to several famous eruptions but nothing traceable to Churchill. “We found sulfate from the eruptions of Katmai in Alaska in 1912, from Tambora in Indonesia in 1815 and from Laki in Iceland in 1783,” Mashiotta said. “If in 803, there was a big eruption of Mount Churchill 300 meters from our drill site, we would have seen sulfate there. And we didn’t.”

The core contains other “gems” as well as clues to the White River Ash. The climate record includes the period of the “Little Ice Age,” a period from 1450 A.D. to 1850 A.D., when the climate dramatically cooled, as well as evidence of “Medieval Warm Period,” from 1000 A.D. to 1400 A.D. The core should even provide a long-term history of dust blown from north-central China across the Pacific Ocean to fall on the Alaskan mountain.

Along with Mashiotta and Thompson, Mary Davis, a research associate with the Byrd Polar Research Center, is working on this project. The National Science Foundation supported this research.

Lonnie Thompson | EurekAlert!
Further information:

More articles from Earth Sciences:

nachricht New technologies and computing power to help strengthen population data
22.03.2018 | University of Southampton

nachricht New interactive map shows climate change everywhere in world
22.03.2018 | University of Cincinnati

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

Modular safety concept increases flexibility in plant conversion

22.03.2018 | Trade Fair News

New interactive map shows climate change everywhere in world

22.03.2018 | Earth Sciences

New technologies and computing power to help strengthen population data

22.03.2018 | Earth Sciences

Science & Research
Overview of more VideoLinks >>>