Final Report Summary - CCMP (Physics Of Magma Propagation and Emplacement: a multi-methodological Investigation)
During the CCMP-POMPEI project, the team developed mechanical and conceptual models to explain previously unanswered basic questions on magma propagating in the Earth's crust. In particular, we developed a numerical code to simulate the ascent of magma from the crust-mantle boundary to the surface and calculate the trajectories. We found:
- Topographic loads, and most surprisingly, effective removals of surface mass due for example to crustal thinning or caldera formation, may play a fundamental role in steering magma pockets (or dikes) through the crust. The propagation is not necessarily vertical: it can be diagonal or horizontal depending on the balance between tectonic forces and topographic loading. This leads to eruptions not occurring necessarily from the central conduits of volcanoes, but offset and sometimes quite distant.
- If the mass redistribution at the surface is significant over large spatial scales (such as during graben formation at continental rifts), the trajectories are strongly inclined. This explains why most magma remains stuck in the crust as lower crustal intrusions. The mechanism works at smaller spatial scales too, such as those related to fault scarps. We explained why eruptions occur on the higher part of the scarp (footwall of normal faults or hanging wall of thrust faults) and are often not related to the fault itself, as previously thought.
- Calderas, resulting from the collapse of the roof of a magma chambers, show a common pattern of edifice stresses that are dictating a special behaviour of the magma at depth. This has strong implications for the forecasting of eruptive vents, that very often do not coincide with the central conduits, rather thet are spread over the volcanic edifice or even outside the caldera.
- There is a close link between the shape of the magma-filled dike and the mechanics of the propagation and the deformation and seismicity induced in the surrounding rock, and the scaling laws of the induced earthquakes.
- Topographic loads, and most surprisingly, effective removals of surface mass due for example to crustal thinning or caldera formation, may play a fundamental role in steering magma pockets (or dikes) through the crust. The propagation is not necessarily vertical: it can be diagonal or horizontal depending on the balance between tectonic forces and topographic loading. This leads to eruptions not occurring necessarily from the central conduits of volcanoes, but offset and sometimes quite distant.
- If the mass redistribution at the surface is significant over large spatial scales (such as during graben formation at continental rifts), the trajectories are strongly inclined. This explains why most magma remains stuck in the crust as lower crustal intrusions. The mechanism works at smaller spatial scales too, such as those related to fault scarps. We explained why eruptions occur on the higher part of the scarp (footwall of normal faults or hanging wall of thrust faults) and are often not related to the fault itself, as previously thought.
- Calderas, resulting from the collapse of the roof of a magma chambers, show a common pattern of edifice stresses that are dictating a special behaviour of the magma at depth. This has strong implications for the forecasting of eruptive vents, that very often do not coincide with the central conduits, rather thet are spread over the volcanic edifice or even outside the caldera.
- There is a close link between the shape of the magma-filled dike and the mechanics of the propagation and the deformation and seismicity induced in the surrounding rock, and the scaling laws of the induced earthquakes.