Inside an active volcano on Montserrat
An international team of researchers has started to collect imaging data on the Soufriere Hills Volcano in Montserrat which erupts regularly since 1995. They're using the equivalent of a CAT scan to understand its internal structure and how and when it erupts. Several years ago, the U.S. National Science Foundation (NSF) funded the CALIPSO project ('Caribbean Andesitic Lava Island Precision Seismo-geodetic Observatory'). The new experiment is dubbed SEA-CALIPSO ('Seismic Experiment with Air-gun source') and 'will use air guns and a string of sensors off the back of a research ship combined with sensors on land to try to image the magma chamber.' Early results are surprising, as said one of the leading scientists: 'The interesting thing is that much more magma is erupting than appears represented by the subsiding bowl.' ...
You can see above a photo taken on December 19, 2008 by 'Dave', a friend of lara68 who uploaded it today on Flickr with this caption: "Dave is in the Caribbean for Christmas, and he sent me this aerial photo of the erupting volcano on Montserrat." (Credit: lara68, via a Creative Commons license) Here is a link to other versions of this very recent photo.
The SEA-CALIPSO project involves several academic institutions and is led by Barry Voight, Retired Professor of Geology and Geological Engineering, and Stephen Sparks, Professor of Earth Sciences at the University of Bristol, UK.
Before going further, the Soufriere Hills volcano began its current series of eruptions and pauses in 1995. It went through three recent eruptive episodes, from November 1995 to March 1998, from December 1999 to July 2003 and from October 2005 to April 2007. As you can see on the recent photo above, it's still active. Here is a link about the first eruption on Montserrat on Voight's website. It made the cover story of Geophysical Research Letters on September 15, 1998.
Now, let's return to a more recent period. How do these researchers find what's inside a volcano? "The measurements taken during the on-going CALIPSO project, the ground-based phase of this study, uses Global Positioning Systems and strain meters to measure the exact up-and-down and sideways movements of numerous points over the volcano island. However, the volume changes represented by those measurements did not match measured volumes of the actual lava flows during the various eruption episodes, raising an intriguing puzzle."
Here are some comments from Voight. "In SEA-CALIPSO, we are using a variety of research tools to image the internal structure of the Earth's crust under the volcano island. Our knowledge of the deeper structure under any of the Caribbean Islands is very limited and the internal structure of an active volcano is one of the most puzzling questions in the Earth sciences. It is nearly impossible to get direct measurements inside the volcano, so we rely largely on remote sensing methods."
So how did they proceed? "The researchers used seismic wave arrivals at over 200 land and sea floor seismometers to give CAT-scan like images of structure to about 5 miles deep. They were also able to map how the seismic energy bounces off key reflecting layers near the crust-mantle boundary, around 20 miles down. The basalt at those depths forms horizontal layers that partly crystallize and generate residual melts enriched in silica, water and sulfur. These melts rise in pulses to shallower levels, where they define magma chambers of andesite composition -- the lava now erupting on Montserrat."
You should read the whole Penn State news release for additional details. But, for more information about this project, here is a selection of links I recommend, in chronological order.
- The Soufriere Hills Volcano (LiveScience's Image of the Day, January 4, 2005)
- Researchers Seek Suspected Magma Chamber Below Active Volcano (University of Arkansas Headlines, April 27, 2005)
- Unprecedented pressure increase in deep magma reservoir triggered by lava-dome collapse (PDF format, 4 pages, 909 KB, link to Geophysical Research Letters abstract, February 2006)
- The CALIPSO Project at Soufrière Hills Volcano, Montserrat, BWI: Using Integrated Deformation Data to Constrain Magmatic Processes (PDF format, 1 page, 54 KB, 2007)
- And finally, the Facebook group about SEA-CALIPSO: Imaging the Magma Chamber on Montserrat
Sources: Penn State News, December 19, 2008; and various websites
You'll find related stories by following the links below.