1. Volcanoes in our Community Where are the volcanoes? Science Std: Geo # 3f

2. As we have covered before……  Volcanoes require some special plate conditions to be in place before they can form  Convergent Boundary  Divergent Boundary  Hot Spots  Forms on the upper plate above the convergence  Rift valleys and mid ocean ridges have volcanoes  Localized area in the middle of plates where volcanoes can form

3. So let’s take a look at some places where volcanoes can form……. Under the Sea ….. There are actually more active volcanoes under the ocean than are on the land above the water Why? All of the ocean basins have a mid-ocean ridge divergent area that is constantly expanding

4. Yes, a rift valley under water…… Rising Magma Plate #1 Plate #2 Flowing Rock Ridge Crest Lithosphere Asthenosphere Rift Valley

5. But we can also have them on land  Volcanoes that erupt on land are much more dangerous than those that erupt underwater  They form volcanic mountain ranges  They form island chains  More chances to hurt people and property  Cascade Mountain range in Washington  The Aleutian Island chain in Alaska  And of course there is always……….

6. The “Ring Of Fire”

7. But we can also have them on land  Did you know that……  Why…..?  4/5 of all the world’s volcanoes on land happen where one plate slides beneath another plate  Plate is heated as it is subducted  The heating forces water out of the rocks  This forces the magma to rise up due to lower density  And feed volcanoes on the plates overhead

8. But we can also have them on land  Where else?  Rift Valleys at divergent plates

9. But we can also have them on land  Where else?  Rift Valleys at divergent plates Mount Kilimanjaro is a good example of a volcano formed at a rift valley

10. But we can also have them on land  Where else?  Hot spots The Hawaiian Island chain is a great example of several volcanoes that came from a hot spot

11. We can look at these volcanoes on maps..

12. Let’s zoom in on an area of the map…. Maps like this can give you information about where the volcanoes have happened in the past