How do magma chambers rise and how are their locations mapped, since it's hard to detect them?

BRY2K

Here is a response to 1 of your Q's: The location of magma chambers can be mapped using seismology: seismic waves from earthquakes move more slowly through liquid rock than solid, allowing measurements to pinpoint the regions of slow movement which identify magma chambers. As a volcano erupts, emptying the magma chamber, the surrounding rock will collapse into it. If a large amount of magma is erupted, causing the chamber to reduce considerably in volume, then this can result in a depression at the surface called a caldera. http://en.wikipedia.org/wiki/Magma_chamber Also: Cyclic layering is a common feature of the ultramafic zone of layered intrusions and is usually attributed to the entry of new pulses of dense magma into the chamber. Since the crystallization of olivine and bronzite lowers the density of the magma, a new pulse of the parent magma will be denser than the fractionated magma in the chamber. If the new pulse enters with excess momentum it will initially rise up into the host magma to form a fountain, then fall back around the feeder when negative buoyancy forces overcome the initial momentum of the pulse. http://petrology.oxfordjournals.org/cgi/content/abstract/30/4/885 Sep 30 09, 11:54 AM