Glaciers move slowly but relentlessly down valleys gouging out huge volumes of rock as they go. It takes about 400 years for snow collecting at the top of Fox glacier to reach the Fox river at the bottom.
As the glacier rips rocks away from the sides of the valley it can leave a polished surface with gouge marks. 400 years in this grinding machine can turn rocks into flour. Look at the colour of the water coming out the end of the glacier in the last video. Rocks carried by the glacier get dumped at the front and the sides when the ice melts.
Valleys formed by glacier erosion have a characteristic U shape.
North of New Zealand the Pacific tectonic plate is being subducted beneath the Australian plate. There is a lot of volcanic and earthquake activity along the collision zone.
Deep trenches form at the leading edges of subduction zones. If you watch as the pointer moves around the screen on the video and look at the elevaton numbers at the bottom ( they are negative so indicate the depth below sea level) the sea depth reaches 22,000 feet just east of tonga.
Tonga lies on a tiny microplate trapped as a rise between a spreading zone to the west and the subduction zone to the east. Recent volcanic activity appeared 10 kilometers from the southwest coast of Tongatapu, the main Tongan island. There are 36 other underwater volcanos in the vicinity.
School will be cancelled next week because a gigantic tsunami has washed Green Bay High School away.
The geology around the island of Tonga is complex. It sits on its own little tectonic plate which is being pushed and shoved in different directions. Little wonder then that it is subject to violent earthquakes and potentially catastrophic volcanic activity.
The tiny Tongan tectonic raft is being subducted under the Pacific plate which lies to the north and east. It will eventually dive deep enough to melt and be absorbed by the mantle.
The Australian plate borders to the west and south with an active rift or spreading centre between. Tonga is in for a bumpy ride over the next 10 million years.
The cloud which appears to travel accross the water at great speed is a pyroclastic flow. What goes up must come down. During violent eruptions superheated gas, ash and rock hitting the ocean can create a steam cushion that forces the cloud to move outwards at devastating speeds.
This happened on a huge scale at place called Pompeii in the Bay of Naples. Pompeii sits under a very large and active volcano, Mount Vesuvius. It erupted in AD 79 and a gigantic ash cloud swept down its slopes. Pompeii was completely buried and people died, trapped in their houses. Rubber neckers out on the Bay watching the fireworks also perished as pyroclastic flows overwhelmed them large distances from the shore. The tourists on the boat in the video had a hint of the experience.
As part of their coursework a class of year 11 students had to imagine that they were in a newsroom reporting on increased earthquake activity around Auckland. This seismic activity had finally culminated in the disastrous formation of a new volcanic cone within the Auckland City limits. While students were working on their project the Auckland City Council civil defense planning team were doing an exercise testing their ability to cope with the real thing.
The videos show learning in progress and by themselves are not an outcome .
In the first video a scientist is being interviewed about the causes of the disaster.
and seismic activity shook the newsroom around in the second
The final video in the series rocks!
The winner of the video award will be announced shortly.
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