The field of volcanology has greatly changed during the last half century. The profession is now much more diverse and interdisciplinary, even including collaborating researchers from the social and medical sciences. This new mode of cooperation and working has been more successful in mitigating volcanic hazards and risks. There are fewer of the strong-willed lone rangers of the past and more of those who work with teams to more effectively understand how volcanoes work to protect those living on or near active or potentially active volcanoes. Moreover, there are more university departments with volcanology in their curricula and more international symposia and workshops focusing on mitigation of risk posed by volcano-related hazards. We all have respected colleagues and volcano observatories in many countries. The importance of understanding explosive volcanic eruptions and tracking of eruption plumes involves volcanologists, atmospheric physicists, and air-traffic controllers and is of great interest to the aviation industry. We now have the links in place between great science and practical applications.

ABSTRACT Hydrovolcanic eruptions occur when rising magma violently fragments while mixing with shallow surface water or groundwater. These eruptions, among the most violent on Earth, generate hundreds to thousands of explosions throughout the course of an eruptive event. Each of these explosions ejects a mixture of juvenile and accidental clasts, gas, and water droplets. The solid materials either fall to the ground from tephra jets or collapse to form pyroclastic density currents (PDCs). The deposits of these eruptions build up rings of bedded tuff around the vent, recording both a wide variety of pyroclastic depositional mechanisms, and important changes in the eruptive style with time. This field trip will explore the deposits of basaltic, hydrovolcanic eruptions in the Fort Rock–Christmas Valley basin, the location of an intermittent, fluctuating, widespread Pleistocene lake (Fossil Lake). Basaltic volcanoes erupted in the center of the lake basin are characterized by Surtseyan eruptions (standing water), along the lake basin margins by maar eruptions (groundwater), and beyond the lake margin by scoria cones. The focus of the trip will be Fort Rock (Surtseyan) and the Table Rock Complex (large Surtseyan-tuff cone, large maar, and seven minor craters). This trip offers the opportunity to examine (1) settings under which explosive hydrovolcanic eruptions occur, (2) depositional characteristics that infer eruptive conditions, (3) a wide variety of pyroclastic deposits (i.e., fallout through air or a body of water, eruption-fed subaqueous sediment gravity current deposits, PDC deposits), and (4) mega-dunes (200 m wavelength dunes associated with large scale, dilute, PDCs from an energetic, mafic hydrovolcanic eruption).

Tuffs have been a part of man's environment for thousands of years and underlie some of Earth's largest cities. There are 41 large industrial cities in 24 nations (including two megacities) that are underlain or partly underlain by tuffs. Rome, one of the world's most famous cities, has a history tied closely to the tuff deposits upon which the ancient city was built. Tuffs are products of explosive volcanic eruptions and are composed of volcanic ash and pumice particles that are bonded by natural cements or are naturally welded; they make excellent building materials and have been proposed as a medium for industrial and nuclear waste storage. Tuff deposits are often hundreds of meters thick and can cover hundreds to thousands of square kilometers. The most common tuffs used for building material are ignimbrites (pyroclastic flow deposits), in which the pumice and glass shards have been sintered by heat immediately after deposition or have been bonded by natural cements precipitated from fluids percolating through the deposits. When used for building stone, ignimbrite is sawn or broken away from a quarry face along natural cooling joints and then fashioned into blocks by hand or with power saws. These blocks, with enough strength for multiple-story buildings, stone walls, and other structures, are resistant to weathering, are lightweight, and have good insulating properties—better than most other natural building stones.

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Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.