Chris Rowan is a geologist specialising in the dark arts of paleomagnetism, and getting people to pay him to travel to exotic destinations for fieldwork. Having drilled up New Zealand during his PhD, and South Africa in his first post-doc, he now works at the University of Edinburgh.
Anne Jefferson has a love of all things water-related and blends hydrology, geomorphology, geology, and climate change in her work. She has a Ph.D. from Oregon State University and is now an assistant professor at the University of North Carolina at Charlotte.Mount Etna has been erupting again, and some fairly impressive footage of lava fountains have made it onto YouTube:
Both clips at some point zoom out to show that the footage is being filmed from the streets of a town in the shadow of Etna, probably Catania, Sicily's second-largest city. Despite their proximity, however, these eruptions actually present very little real danger to the population, because unlike other volcanoes in the western Mediterranean region like Vesuvius, Etna tends to erupt runny basaltic lava flows rather than periodically blowing its top, so whilst there's always a risk of flows overwhelming property, they move so slowly that the people can get out of the way.
When you actually consider the tectonic setting of Etna, this is actually quite odd. The western Mediterranean has had a complicated geological history, but most of the Italian volcanoes appear to be related to the westward subduction of oceanic crust. Water and gases released from the subducting plate trigger melting, and are incorporated into the resulting magma: this generally leads to explosive volcanism. In contrast, less viscous basaltic magmas are generally the result of the melting of unaltered mantle, either due to decompressional melting at rift zones or extra heating by rising mantle plumes (as in the case in Hawaii).
Unfortunately, I'm not in a position to research the whys and wherefores of this anomaly right now. I vaguely recall reading something about the possibility of a slab window - a break in the subducting plate which allows unaltered mantle material to rise to the surface - but I can't remember the details or even if its relevant. Perhaps one of my geoblogging colleagues can provide the answer...
Comments
I think I read an article about Etna in American Scientist, maybe a couple years ago? I don't know if it talked about the eruptive style in relation to tectonic setting, though. (I think I would have remembered if it did... but maybe not.)
I used to teach an Earthquakes and Volcanoes class, and I often wondered what was up with Etna. (I was essentially substituting for someone else - "She does structure and petrology, therefore she knows about earthquakes and volcanoes! She can teach 'Shake and Bake' while X is on sabbatical!" was pretty much the logic.)
Does the geoblogosphere have an igneous petrologist or volcanologist? I don't think I've seen one around - and volcanoes would be such a great blogging topic. (*drops bait in front of various lurking geologists*)
Posted by: Kim | September 7, 2007 3:21 PM
Same thing happened with the friendly neighbourhood local active volcano (Tarawera) where I grew up -- an atypical basaltic blip in the middle of a ignimbrite/andesite region right above a subduction zone. You can get both on the same boundary though, because the Auckland region, which lies over a rather deep part of the same subduction zone, only has basaltic volcanoes.
What do I know, I'm a biologist :)
Posted by: Chris | September 8, 2007 1:47 AM
Chris, here's a story you might like.
Posted by: Mo | September 11, 2007 8:24 AM