Peering into the Mouth of a Volcano
By Dr. Sven Friedel, FEMLAB Gmbh
We generally look upon volcanic eruptions as being unpredictable, and one reason we label them as such is that volcanoes are so complex. Nevertheless, these impressive natural displays, which threaten an increasing number of people, are the result of deterministic physical and chemical processes. In principle, it is possible to express these processes through PDEs, but the complexity of the interactions among these effects alone can make it diffi cult to fi nd an appropriate mathematical expression. Powerful simulation with COMSOL gives volcanologists deeper insights into volcanic processes and moves them a step closer to more accurate predictions.
In this 3D model (top) of the Merapi volcano, water infiltration into the fractured conduit
casues a specific pattern of electrical voltages and magnetic fields. Scientists use this model to infer volcanic activity and processes
and improve the prediction of eruptive crises.
Sven Friedel places sensors near the crater of Merapi volcano, located in central Java, which has erupted as recently as 2001.
These sensors measure the electrical field, providing values against which he can verify the COMSOL model.
A group of scientists from the Univ. of Leipzig, the ETH Zurich and the IPG Paris are researching how to use information about electromagnetic fields in volcanoes to investigate and observe their activity and ultimately predict volcanic crises. They are focusing on the electrical potential that arises from the flow of gases and water in porous rock. The scientists suspect that these flows are sensitive indicators of changes in the volcano's structure, indicators that can appear long before mechanical changes or even eruptions. By measuring changes in the electric field, the researchers hope to infer which flows are the cause and thereby gain knowledge about activity within the volcano.
The interpretation of field measurements and the optimization of the investigative strategy require the numerical simulation of the underlying processes. The demands on a suitable simulation tool are high. First, it must have multiphysics capabilities, that is, the ability to couple multiple nonlinear physical effects, in this case including hydraulic flow and electromagnetic fields. In addition, the software should allow researchers to expand standard PDEs with new terms. Finally, it is necessary to carry out the calculations in a realistic 3D model. These requirements led the scientists to turn to COMSOL.
Sven Friedel (left) joins Carsten Rücker (center) and Thorsten Winger (right) from the Univ. of Leipzig to examine the solar cell that powers a continuous monitoring station and its radiotelemetry equipment.
The COMSOL model the scientists arrived at allows them for the first time to investigate the processes underlying the interactions between flow and electromagnetic fields. In the past, they had no real understanding of what was happening below the earth's surface and why the volcano behaved as it did. Now, however, they can more easily perform what-if analyses and create models with a true 3D topography that combines the many physical processes that occur in volcanoes. For the first time we were able to run a simulation of a coupled fluid flow, the electrical currents created by it, and the resulting magnetic field. This represents a threefold-coupled problem in a complicated 3D elevation model of a volcano.
Even though the simulation is based on numerous assumptions and simplifications, it points the way towards more complex and realistic models. A volcano system involves many intercoupled physical processes including heat transport, material transport, phase changes as well as chemical reactions. The next challenge for this electrokinetic simulation is accounting for the heat balance, which will lead to more realistic flow systems including the effects of hydrothermal convection cells and the multiphase flow of water and steam.
A final challenge for volcano studies and observations is in taking field measurements to support these new types of electromagnetic-based volcano models. Here, too, simulation calculations can contribute considerably to the optimization of the sensor systems.
Note: This article is based on research by Dr. Sven Friedel, now general manager of COMSOL's Swiss office, and part of this material has appeared in the German magazine Physik Journal (3/2004, Nr. 11, pgs 62-63). In addition, a basic version of Dr. Friedel's model is included in the Model Library that accompanies the COMSOL Earth Science Module. Interested parties can view this model and its results by requesting a copy of the COMSOL Multiphysics Viewer from your local sales representative or by sending an email to info@comsol.com.