Hydrovolcanic explosions; II, Evolution of basaltic tuff rings and tuff cones

摘要: Eleven basaltic volcanoes from a variety of geologic settings were studied in order to compare vent morphology, deposit stratigraphy, and emplacement mechanisms at tuff rings with those cones. The consist thinly bedded, poorly indurated, relatively fresh pyroclasts deposited bedding angles less than 12 degrees. Highly inflated pyroclastic surges are the dominant means emplacement, as evidenced by abundance sandwave bed forms. cones massive, thickly highly hydrated up 30 This massive contains ash-fall layers interspersed nearly equal volumes base-surge beds, result intermittent Strombolian Surtseyan activity. A complete spectrum explosive volcanic activity, phreatic magmatic, results shallow-to-moderate depth interaction magma external water sources. venting phenomena range single burst that produces an explosion breccia prolonged series explosions various energies produce complex interbedded fall surge beds. Stratigraphic data models suggest cool (below 100 degrees C), wet emplacement. In contrast, thinly-bedded deposits typically emplaced while hot (above C) dry. As volume explosively mixes increases, amount steam produced but level superheating decreases. leads increased "wetness" resulting blasts. With increasing ratios magma, activity changes lava fountains dry surges. landforms respectively cinder cones, rings, Accordingly, environment would contain cones; abundant ground promotes rings; shallow body standing favors development