Volcanoes are produced over lithosphere cracks and mantle hot spots. Hot spots are rising plumes of hot mantle magma. As tectonic plates move over the hot spot, a chain of progressively younger volcanoes is formed opposite to the direction of plate movement. Volcanic island chains and volcanic belts are created on the overriding plate, parallel to the direction of the moving oceanic plate. Geological Events 18.2 VOCABULARY volcano hot spots volcanic belt volcanic island arc earthquakes fault focus epicentre shallow-focus intermediate-focus deep-focus seismic wave body wave primary wave (P–wave) secondary wave (S–wave) surface wave

Earthquakes result when tectonic forces overcome the friction between plates. Earthquakes are categorized based on how far beneath the surface the focus is located. The sudden movement of the lithosphere during an earthquake sends seismic waves (vibrations) through Earth. Primary and secondary body waves travel through Earth, starting at the focus, the site of the earthquake within Earth. Surface waves travel along the outside of Earth. They cause the most destruction. Geological Events 18.2 VOCABULARY volcano hot spots volcanic belt volcanic island arc earthquakes fault focus epicentre shallow-focus intermediate-focus deep-focus seismic wave body wave primary wave (P–wave) secondary wave (S–wave) surface wave

 A Volcano marks a spot where there is a crack in the lithosphere. a.They can form at mid-ocean ridges where plates are being pulled apart, and magma rises up. Geological Events 18.2

 A Volcano marks a spot where there is a crack in the lithosphere. b. They can also form about 200 km from a trench, when trapped water becomes steam and melts through the crust. This forms volcano belts on continents and volcanic island arcs in the ocean. Geological Events 18.2

 A Volcano marks a spot where there is a crack in the lithosphere. c. They can form above a hot spot in the mantle, caused by heated concentrations of radioactive substances near the Earth’s core, causing hot columns of rising mantle that melt through the crust. Geological Events 18.2

 Hot Spots A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands. Hot spot evidence supports that the plates move over the Earth’s surface Geological Events

 Earthquakes happen when two tectonic plates move past each other. The plates do not have smooth edges so there is tremendous friction that keeps them from sliding...until enough pressure builds up, and then the plates move suddenly. This sudden movement is what we call an earthquake.  The boundary where the two plates move past each other is called a fault. Geological Events 18.2

 The location of the earthquake is called the focus. The focus can be deep in the earth or relatively shallow down. It depends which part of the two plates slide past each other.  The epicenter is the spot above the focus, on the surface of the Earth. Earthquakes are categorized according to the depth of their focus. Geological Events 18.2

 Plotting epicenters on a map (this data: ) clearly outline some of the plate boundaries. Geological Events 18.2

 Earthquakes travel through the Earth in wave form. These are called body waves and there are two kinds: a.Primary waves (P-waves) are waves that travel parallel to the direction of the wave. They are a ‘compression’ wave. They are like pulling on a spring and letting the end go. It stretches and compresses. They can travel through all parts of the Earth. b.Secondary waves (S-waves) are waves that travel sideways (shear) to the direction of the wave. They are like a slithery snake. They can only travel through the mantle and the crust. They cannot travel through the core. Geological Events 18.2

 The most destructive kind of earthquake wave is called a surface wave. They travel along the surface of the crust like a wave on the ocean. They are what destroy buildings, bridges, etc.  Scientists use instruments called seismographs to measure the strength of earthquakes. They use the Richter scale. Each increase of 1 on the scale means that the earthquake is 10 times as strong. An earthquake of 5 is 10 times stronger than a 4. Geological Events 18.2