EARTHQUAKES & VOLCANOES

EARTHQUAKES Vibrations in the ground that result from movement along breaks in Earth’s lithosphere called faults

WHERE DO EARTHQUAKES OCCUR? Most earthquakes occur along plate boundaries

TYPES OF FAULTS Normal forces pull two blocks of rock apart ex. divergent plate boundary Reverse forces push two blocks of rock together ex. convergent plate boundary Strike-Slip two blocks of rock slide horizontally past each other ex. transform plate boundary

EARTHQUAKE EPICENTER Seismic Waves - Energy that travels as vibrations on and in the Earth Focus – where seismic waves originate and where rocks first move along the fault Epicenter - location on the Earth’s surface where the seismic waves originated

TYPES OF SEISMIC WAVES Primary (P) Waves move in a push-pull motion like a spring fastest-moving waves and the first waves you feel Secondary (S) Waves move in an up-and-down motion slower than P waves do not travel through liquid Surface Waves travel only on Earth’s surface in a rolling motion most destructive

STUDYING EARTHQUAKES Seismologist – scientist that studies earthquakes Seismometer – instrument used to measure and record ground motion Earthquake Scales: Richter Scalemeasures ground motion Moment Magnitude Scale measures total amount of energy released by an earthquake Modified Mercalli Scale measures and describes damage resulting from an earthquake

VOLCANOES A vent in Earth’s crust through which molten rock ( magma ) flows Once magma reaches the surface it is called lava

FORMATION OF VOLCANOES Most volcanoes form at plate boundaries Convergent as one plate subducts beneath another the rock melts and rises to the surface Divergent As the plates separate magma rises through the vent in Earth’s crust and forms new crust ex. sea-floor spreading

HOT SPOTS Volcanoes not associated with plate boundaries convection currents in the mantle rise magma to the surface as plates move over the hot spot island chains are formed The oldest island is the farthest away from the hot spot ex. Hawaiian Islands

TYPES OF VOLCANOES Shield Volcano large, with gentle slopes form along divergent boundaries or hot spots Composite Volcano large and steep-sided resulting from explosive eruptions form along convergent boundaries Cinder Cone Small, steep-sided

VOLCANIC ERUPTIONS Quiet Eruptions magma has a low viscosity (low silica content) Violent Eruptions magma has a high viscosity (high silica content)

EFFECTS OF VOLCANIC ERUPTIONS Pyroclastic Flow fast-moving avalanches of hot gas, ash, and rock that can reach speeds of up to 100 km/h and temperatures of up to 1000 °C Lava Flows Ash Fall Mudflows