Presentation on theme: "Chapter 11 Earthquakes and Volcanoes. Earthquakes l The shaking caused by the sudden movement of the crust l Scientists estimate that over one million."— Presentation transcript:
Chapter 11 Earthquakes and Volcanoes
Earthquakes l The shaking caused by the sudden movement of the crust l Scientists estimate that over one million earthquakes happen every year. l Approximately one earthquake every thirty seconds. l Most so small that no one notices them are recorded by seismographs.
l Several thousand per year actually move the surface of the Earth. l About 20 per year cause severe changes in the Earths surface. l These have the potential to cause serious damage to buildings and dramatic loss of life in populated areas.
Seismic Waves l Waves travel from the break outward. l Main cause is faulting. l If they occur on the ocean floor they can cause giant waves called tsunamis – Travel at km/hr – 10 to 20 meters high when they hit the coast.
Seismic Waves l Focus- where the rocks break – below ground l Epicenter- the surface directly above the focus. l Where shaking is worst
Seismic waves l Three types l Primary waves- P waves – Fastest – Travel through solid, liquid, and gases – Pressure wave l Secondary waves- S waves – slower – Dont go through liquids – Shear waves - side to side
Seismic waves l Surface waves- L waves – slowest – Move like ocean waves - rise up and down – cause the most damage
Seismograph l Detects and measures seismic waves l Seismogram is the record made by it l Studied by a seismologist l Flat line - no motion l Bigger waves, stronger quake
Richter scale l How we compare the strength of earthquakes l Not a machine l Number from 1 to 10 l Higher number stronger earthquake. l Every 1 number higher is 10 times stronger l Bigger than 6 very destructive
Predicting Earthquakes l To be useful must predict – where – when – how strong l Not very good l make buildings differently in earthquake areas l Trying by measuring motion of earth, speed of waves, tilt of earth, electricity
Volcanoes l Magma- melted rock below the surface l Lava- when it reaches the surface l Volcano - where lava reaches the surface l Lava lets us see what is below the crust l Different types of lava l Dark colored, runny lava flows quietly l Light colored hardens inside, pressure builds and it explodes. l Gas bubbles can form pumice and scoria
Rock fragments l Thrown out in eruptions l Different sizes l Volcanic dust- like flour l Volcanic Ash- grains of rice l Cinders- about the size of a golf ball l Volcanic bombs- a few centimeters to several meters across
Types of Volcanoes l Three different types l Cinder cone formed by piling up rock fragments from explosive eruptions l Narrow base and steep sides l Shield volcanoes runny lava pouring out covers the ground in layers l large area, gentle slope - Hawaii
Types of Volcanoes l Composite Volcano- Alternating layers of rock caused by alternating types of eruptions l Explosive lays down rocks l then covered by lava, l Another explosion, l More lava l etc. l large cone shaped mountain forms
Volcano Parts l Vent- The pipe that the lava flows through l Crater- funnel shaped pit at the top of a volcano l Caldera- If the walls of the crater collapse and the crater becomes very large.
Volcano Zones l Ring of Fire- all the way around the Pacific Ocean l Through the Mediterranean Sea l Mid-Atlantic Ridge- Underwater Mountain range down the middle of the Atlantic Ocean