Earthquakes & Volcanoes

Objectives Given information on Earthquakes, you will be able to describe, in writing: a) what an earthquake is; b) what the elastic rebound theory is; c) how earthquakes are measured; d) how earthquakes are related to plate tectonic theory; e) hazards associated with earthquakes; and f) the significance of studying earthquakes. Given information on Volcanoes, you will be able to describe, in writing: a) what a volcano is; b) what types of volcanoes there are; c) how volcanoes are measured; d) how volcanoes related to plate tectonic theory; e) hazards associated with volcanoes; and f) the significance of studying volcanoes

Earthquakes Definition: An earthquake (also known as a tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves.

Earthquakes Elastic Rebound Theory explanation for how energy is spread during earthquakes plates/blocks of earth shift on opposite sides of a fault these are subjected to force (Time 1) they accumulate energy (Time 2) they slowly deform until their internal strength is exceeded a sudden movement occurs along the fault accumulated energy is released rocks snap back to their original undeformed shape (Time 3)

Earthquakes Measurement 1. Magnitude scale a) measures energy released; b) an earthquake one number higher is approximately 30 times more powerful (e.g. a 7.0 vs. a 6.0); (the scale is logarithmic) d) an earthquake one number higher produces approximately 10 times more ground shaking e) examples = Moment Magnitude, Richter

Earthquakes Measurement (cont.) 2. Mercalli intensity scale a) measures intensity or damage of an earthquake; b) quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures d) scale ranges from I through XII, with I denoting a weak earthquake and XII one that causes almost complete destruction e) based on the amount of resulting physical damage received f) data is gathered from individuals who have experienced the quake

Earthquakes Plate Tectonics Earthquakes are NOT randomly distributed across the globe They are concentrated along narrow zones Most earthquakes (~80% or more) occur along plate boundaries Interior of plates are mostly earthquake free Earthquakes define plate boundaries Some also occur at Hot Spots

Earthquakes Hazards Ground motion Liquefaction Landslides & mass wasting Tsunamis

Earthquakes Significance It is important to study earthquakes due to the loss of life and damage to property they can cause Human population continues to grow and many cities are cited along plate boundaries Education is the key to being prepared for earthquakes

Volcanoes Definition A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time.

Volcanoes Types There are 5 general types of volcanoes: 1. Caldera volcanoes 2. Cone volcanoes 3. Lava Dome volcanoes 4. Shield volcanoes 5. Strato volcanoes

Volcanoes Types of Eruptions 1. Effusive (Hawaii) 2. Explosive a) Pyroclastic Flow b) Phreatic Eruption c) Plinian Eruption d) Strombolian Eruption e) Vulcanian Eruption

Volcanoes Measurement The Volcano Explosivity Index (VEI) provides a relative measure of the explosiveness of volcanic eruptions. The scale is based on: Volume of products erupted eruption cloud height qualitative observations

Volcanoes Plate Tectonics Volcanoes are NOT randomly distributed across the globe They are concentrated along narrow zones Most volcanoes (~80% or more) occur along plate boundaries Interior of plates are mostly volcanoe free Volcanoes help to define plate boundaries Volcanoes form Hot Spots

Volcanoes Hazards 1. tephra (ash fallout) 2. pyroclastic flows (Mt. Unzen, Japan) 3. tsunamis (Krakatau) 4. mass wasting (landslides) 5. lahars (volcanic mudflows) 6. lava flows (Hawaii) 7. gas emissions (Mammoth Lakes) 8. directed blast (Mt. St. Helens) 9. pyroclastic surge (less dense than pyroclastic flows)

Volcanoes Significance It is important to study volcanoes due to the loss of life and damage to property they can cause Human population continues to grow and many cities are cited along plate boundaries Education is the key to being prepared for volcanoes

Summary Earthquakes occur due to the elastic rebound theory; they are measured using the magnitude scale; they occur along plate boundaries; they cause ground motion, tsunamis, mass wasting, and liquefaction all of which may cause loss of life and damage to property Volcanoes occur due to molten rock reaching the earth’s surface; they are measured using the VEI scale; they occur along plate boundaries; they cause pyroclastic and lava flows, ash fallout, lahars, mass wasting, earthquakes, and may cause tsunamis, all of which may cause loss of life and damage to property