ablock_usgs_gov

Good eye. The flows from a collapsing dome are scary, man. Is the one you saw of Unzen in 1991? Blocks fall off the dome , hit the talus slope below and just explode into dust, fragments, steam and gas. The whole mass races down the slope. My simple understanding - and I speak under correction from my learned colleagues with petrological expertise on this thread - is that the dome rock is hot, fragile and charged with hot gas under great pressure. When it falls and hits, it blows itself apart. The hot fragments surge downhill propelled by the explosion, aided by gravity and gliding on a cushion of trapped air, gas and steam. Note - heres an open invitation to my colleagues to comment. My understanding of this is just enough to keep me out of the way when it happens.

Hola back to Bob. Steve is retired and loving it; we don't see him at the office too often. Barb changed up Murrays trouseau years ago. Brian will address your more technical query...

Andy

I was at Pinatubo and hope I never see anything as big as that again. I've seen a bunch of smaller ones, or the aftermath of smaller ones. Any eruption that kills people is too big for my taste. I'm afraid that for me volcanoes are the enemy, not the source of breathtaking majesty and wonder they are for others. - Andy

Thats a good question that occupies a lot of our time. Think of it this way: magma 'floats' up to the surface, propelled by bouyancy and gas. As it rises, it forces rock out of the way, deforming the surface. If the rock is brittle and the force of the rising magma is great enough, the rock breaks. If heat gets close enough to the surface, it boils groundwater. So to know if a volcano might erupt we look for gases, deformation of the ground and earthquakes.

Building on that, I work on the Volcano Disaster Assistance Program along with others on this thread. We work with volcano observatories in the developing world to help them mitigate volcano hazard. We don't have the primary monitoring responsibility for any overseas volcanoes but are available for consultation if one of the observatories we work with asks. That might be answering simple questions or dealing with tough , complicated scenarios. So sometimes we are looking into other volcanoes quite closely -and in real time- along with our foreign partners, but for the most part we just have a more collegial or advisory role.