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eklemetti | July 4, 2010So, I've had requests on the blog to help to do some defining of volcanologic terms on the blog, so I thought I'd try a new column called Eruptions Word of the Day. I'm not sure how often it will run, but let's give it a try.
Eruptions Word of the Day for July 5, 2010: Dacite
Dacite is a magma type defined by silica (SiO2) content between 63-68 (or 69) weight percent. That is the textbook definition, but some other typical characteristics of dacite lavas (or magmas) is the presence of certain minerals: plagioclase feldspar and hydrous minerals (containing water in their mineral structure)…
eklemetti | March 31, 2010As a volcanologist, I am partial to impressive lava flows, especially in volcanoes that erupt material that you'd think wouldn't produce big flows. For example, there are quite a few volcanoes in the Chilean Andes that erupt dacite lavas, which are relatively viscous (sticky), so you might expect it to erupt explosively. However, you can get large dacitic to rhyolitic lava flows, quite commonly, and these large flows are called coulées (a "volcanic dome flow").
Lllullaillaco volcano on the Chile/Argentina border. Note the very prominent coulée with flow levees. Click on the image to see a…