Volcanoes

We talked about volcanoes today, and why subduction zone volcanoes are generally more explosive than hot spot volcanoes. The reason for this explosiveness is generally high viscosity, a property that slows the flow of magma and causes build-up of gasses below the earth's surface. Pressure builds in the magma chamber until the crust can no longer hold together. The release of this extreme pressure is explosive and sends a huge cloud of rock and ash into the air. The expelled material, called tephra, accumulates on the slopes of the volcano and further away depending on its size (larger particles stay closer while smaller particles, like ash, may travel hundreds or thousands of miles).

Check out this awesome website about volcanoes as part of your homework for Thursday!

http://volcano.oregonstate.edu/

Remember, the plan for the week is this:

Monday night: Chapter 3 Sections 1 and 2. Draw a picture that illustrates one of the key concepts.
Tuesday night: Read Section 3
Wednesday night: Read Section 4 and the different sections of the website above!

Here's a diagram of a stratovolcano from this website (http://serc.carleton.edu/images/research_education/trail_guides/typical_volcano.jpg)

You can see the years of built up rock layers: those are from accumulated ash and rock fall, as well as from lava flows down the side of the cone. The steep sides of this volcano are characteristic of stratovolcanoes: shield volcanoes have relatively flat sides because the lava's low viscosity allows it to flow for a long distance before stopping.