Geog Blog: Tectonics

We are off to an excellent start with both years 9 and 10 battling it out with tectonics. A good singalong is always a good way to start a lesson and of course provide us all with a general overview!

Now that you cant get the Mt St Helens tune out of your head perhaps this is the best time to look at the good old BBC and see what they have to offer in the way of a more technical explaination.
Earthquakes, Volcanoes and Tsunamis are all demonstrated here with clear and easy to understand diagrams and animations.

Mount St Helens erupted on May 18th 1980 following a period of activity which began in March 1980 with an earthquake measuring 4.0 on the richter scale. What followed was 3 months of seismic activity as magma rose within the mountain. As the magma rose, a large bulge grew on the north flank of the volcano, this was due to a blockage in the main vent resulting in the growth of a cryptodome (mound of viscous lava) in the side of the volcano.

On May 18th, an earthquake measuring 5.1 on the richter scale caused a landslide on the northern flank of the volcano, which in turn exposed the cryptodome below, resulting in a sudden release of pressure and a cataclysmic eruption in the form of a lateral (sideways) blast.

The blast zone consisted of 230 square miles with the eruption leaving a 'lunar' landscape in its wake. The effects of the eruption included:
* laval flows and ash filling in Spirit Lake and log jams and ash blocking the channel of the Toutle River;
* 57 people died in the eruption - most from poisonous gases;
* large number of wildlife were killed by the blast and the volcanic ash with nothing surviving in the blast zone
* flooding resulting from blocked rivers washed away road and rail bridges
* crops were ruined and livelihoods of loggers were devastated with large areas of trees being flattened like matchsticks.

These websites will provide you with an excellent source of information for the homework which is due in next week.
USGS Information on Mt St Helens
Wikipedia 1980 eruption of Mt St Helens is an excellent place to start your research
The Mount St Helens National Volcanic Monument has lots of tourist information and webcams.
Mount St Helens National Volcanic Monument library has lots of interesting photographs.

The following videos should also provide you with a good overall understanding of the main issues.