Abstract

The transport network by which magma leaves its mantle source region and rises to the surface to erupt (or not) is hidden from direct observation, and largely occurs on time and spatial scales that are outside the human experience. Our knowledge of magma transport pathways, and the coupling of magmatism to other Earth systems, is thus built on indirect evidence. I will talk about two attempts to relate such evidence to subsurface magma dynamics.

First I will discuss wave propagation within magma-filled conduits, and the coupling of fluid oscillations to surrounding elastic host rocks that may produce long period (10s of seconds) seismic signals observed at many active volcanoes. Specifically, I will use seismicity associated with ongoing rockfall events at Halemaumau, Kilauea, HI, to study the excitation of resonant modes in a column of bubbly magma. I will suggest that total magma volatile content and non-equilibrium degassing control conduit resonant modes, and thus are imprinted on the periods and decay rates of seismic signals.

Second, I will discuss the focusing of magmatism at convergent plate margins to a narrow band of volcanoes at the surface, and the spatial migration of this “arc front” over millions of years away from the plate interface. I will use a combination of geochemical evidence and geodynamic modeling to suggest that arc front migration arises from magmatic lithospheric thickening, modulated by tectonic compression or extension within the upper plate.

Leif Karlstrom and Eric M. Dunham Excitation and resonance of acoustic-gravity waves in a column of stratied, bubbly magma, Under review,JFM

Karlstrom, L., C.-T. A. Lee, and M. Manga (2014), The role of magmatically driven lithospheric thickening on arc front migration, Geochem. Geophys. Geosyst., 15, 2655–2675, doi:10.1002/2014GC005355.