Presentation on theme: "Earthquakes The Richter scale is used to measure earthquake strength."— Presentation transcript:
1 Earthquakes The Richter scale is used to measure earthquake strength. The Richter scale is logarithmic.7.0 is 10 times stronger than 6.08.0 is 10 times stronger than 7.0etc…Therefore 8.0 is 100 times stronger than 6.0.Question:An 8.0 earthquake on the Richter scale releases ___________ times as much energy as a 2.0 earthquake.
2 HOW ARE THEY ALL RELATED? Plate tectonicsEarthquakes & VolcanoesHOW ARE THEY ALL RELATED?
3 EVIDENCE for Plate tectonics Several pieces of evidence support the theory of plate tectonics:Africa and South America were once part of a larger continent (called Pangaea) note similarities in continental shape presence of Mesosaurus fossils
6 Evidence Continued Earthquakes and volcanoes occur along plate boundaries **(where one plate is moving relative to another)
7 ** Side noteVolcanoes also occur above “hot spots” in the middle of lithospheric plates. The hot spot remains in the same location while the plate above moves overtop
8 Evidence Continued Magnetism and spreading centres as plates spread apart, new rock* is formed and older rock moves away from the spreading plate boundary* The rock crystallizes and records the magnetic field of the earth at that particular time
10 VolcanoesComposite volcanoes - this is the stereotypical volcano, erupting and belching smoke and ash everywhere,found along converging plate boundariesLayers of ash and thick lava (magma) form a tall cone.As magma reaches the surface, it cools, hardens and traps gases below.Pressure builds, eventually there is an eruption.See pages
11 Shield volcanoes - these are NOT found at plate Shield volcanoes - these are NOT found at plate boundaries, but instead form over hot spots (a weak spot in the normal lithosphere). Flash AnimationThin magma/lava flows out from a hot spot and forms a low, wide cone.The Hawaiian Islands are an example of a chain of shield volcanoes.Rift eruptions - these occur along long cracks in the lithosphereNot explosive, but release massive amounts of lava.Found at diverging plate boundaries