Are there measurement techniques that can help determine the exact geometry of a volcanic vent?

Question

In a previous question What happens to the higher frequency content of the tremors associated with a volcanic eruption?, I asked about the high(er) frequency content of a volcanic eruption.

In the same vein, I'm interested to know more about the influence of the geometry of the magma column on this particular frequency content and the methodologies that researchers use to take measurements of circular vents. Assuming a uniform cylinder all the way to the magma chamber would aid in the mechanical modeling, but I'm sure this betrays quite a bit of the changes in diameter that take place along the way.

Are precise measurements of the vents/magma conduits of volcanoes currently possible, or is this too big of a risk to personnel and equipment? Which particular techniques (e.g., radar/sonar) would work without having to actually enter the chamber?

Answer 1

Interferometric synthetic aperture radar (or InSAR) is a remote sensing (airplane or, more commonly, satellite) radar techinque used to measure surface deformation. Repeated measurements of radar amplitudes over a common area are used to estimate changes to surface topography. InSAR measurements of surface changes have been used with numerical models of dyke propagation to model magma chambers in the East African Rift System.

Other geophysical methods that can be used to image/model active magma chambers include seismic interferometry, magnetic and gravity methods. Here is a recently published example from Japan which used seismic interferometry to image an active magma chamber. Magnetic and gravity measurements can be taken from airplanes, which may be a bit safer than being on the ground. If the magma chamber has magnetic/density properties different from the surrounding country rock, then mag/grav forward/inverse modelling could be used to create a model of the magma chamber geometry.