Sunday, September 16, 2007

Boat_trip 012


Boat_trip 012
Originally uploaded by Cooky2


Thanks to Geonet NZ.

Photograph of the interior structure of a rhyolite dome, showing a radial pattern of cracks formed as the lava cooled. (Mason’s Rock on the north shore of Lake Taupo)

The main hazards of dome growth are tephra fall from explosive eruptions and avalanches of hot lava from the sides of the dome.

Volcanic gases and acid rain

Gases are the driving force of explosive eruptions. The main gases are water vapour and carbon dioxide, with small amounts of sulphur, hydrogen and other gases. These gases rarely pose a direct threat as they quickly mix with the air and are diluted as they blow downward. Some of the gases, such as sulphur dioxide and hydrogen fluoride mix with water droplets in the eruption plume to form acids which will attack skin, clothing and metals. Rain falling from an eruption plume may be very acidic and this acid rain will attack foliage and crops over a wide area, perhaps even greater than the fall of tephra. The acid rain may also contaminate water supplies. Acidic water is not a major health hazard, but the acid may leach lead from nailheads and flashing on roots and lead poisoning may result. There is the remote possibility that heavy gases (mostly carbon dioxide) emitted before or after an eruption will collect in low-lying areas or confined valleys and cause suffocation. Generally there is enough wind about the lake area to disperse any gas cloud that may form.