One available clue that may contain useful information about the magmatic processes that occur within a subduction zone comes from the position of the volcanoes themselves. In map view, the volcanoes are arrayed in arcs that sit above the subducting slab. Earthquakes within the slab have allowed scientists to determine the depth of the slab beneath the arc of volcanoes. Compiling this depth for all the world's volcanic arcs, and comparing it with the rate of descent of each slab into the mantle produces a striking trend: faster descent produces arc volcanoes over a shallower point on the slab, while slower descent leads to large slab-depths beneath the arc. A hypothesis to explain this trend was recently published; it states that the volcanoes form at a position determined by the temperature structure of the mantle beneath, and by the details of magmatic flow. In particular, it proposes that the hottest magmas that are produced in the subduction zone rise toward the surface, and create a hot conduit that other melts follow. The arc volcanoes are found on the surface, directly above the conduit.
Testing this hypothesis requires a physical/mathematical model of how magma moves through the mantle, and how it transports heat. Previous models of subduction zones have not included the flow of magma, mostly because it was too challenging to compute. To overcome this challenge, we have assembled a team of four scientists with complementary expertise in software engineering, mathematical modelling, fluid dynamics, and geophysics. Together we have the skills to create a new generation of computer model that will describe the flow of magma within a subduction zone. This model will allow us to test the hypothesis described above, as well as other, competing hypotheses. Developing the model will require a multi-stage assembly process, in which each component of the software is designed, written, and tested separately. In this proposal we detail a carefully planned series of tasks that culminate in our ultimate goal of a model of subduction zone magmatism and the position of volcanic arcs. Along the way, we intend to make our software available to other scientists for their use, with the hope that they might help us to improve it. After three years of work with help from two assistants, we'll have new knowledge about subduction, and new mathematical tools for research.
The flow of fluids through porous rock is also of key concern to the growing industry of carbon capture and storage (CCS). One of the leading suggestions for mitigating climate change is the storage of carbon dioxide deep underground in depleted oil reservoirs or saline aquifers. The carbon dioxide at these depths behaves as a supercritical fluid, and it is crucial that we understand how it will move through the reservoir if this technology is to be useful. Our tools will undoubtedly help in this task.
Volcanoes capture the public's imagination, particularly among children. They are an important natural hazard, and while we may think we are immune from the effects of volcanism living in the UK, the recent closure of UK air space by the Icelandic eruption demonstrates that this is not the case. Insurance companies would certainly like to know more about volcanism. Our main focus in this project is on understanding the origin of subduction zone volcanism by studying the processes occurring at great depths within the Earth's mantle, to understand how melting first begins and how that melt is transported to the Earth's surface. This fundamental research will lead to a better understanding of volcanism in general, and eventually to a better understanding of the natural hazard.
|Description||We have developed novel techniques for solving the partial differential equations describing melt migration in partially molten rock.|
|Exploitation Route||Our code is being made freely available, and our tools and techniques will be of great use in building future simulations of subduction zone volcanism.|
|Description||AGU Fall Meeting|
|Form Of Engagement Activity||A talk or presentation|
|Part Of Official Scheme?||No|
|Primary Audience||Other academic audiences (collaborators, peers etc.)|
|Results and Impact|| A poster presentation by Laura Alisic on Shear banding in a partially molten mantle
|Year(s) Of Engagement Activity||2013|