Chapter 21 Section 2 Earthquakes & Volcanoes pp. 738-746

Earthquakes Occur due to plate movement faults Introduction to Earthquakes It’s an Earthquake Song

Earthquakes: Focus vs. Epicenter Focus: point UNDER Earth’s surface where waves originate…along the fault line Epicenter: point ON Earth’s surface directly above the focus…surface waves begin here and move outward Focus of an Earthquake

Seismic Waves 3 types of seismic waves: P-waves S-waves Surface waves Seismic Waves Song

P-Waves P (primary)-waves: move the fastest Rocks are squeezed & pushed in direction of wave (longitudinal) P-Wave Animation

S-Waves S (secondary/shear)-waves: rocks move at right angles (transverse) to direction of waves Slower than P-waves S-Wave Animation

Surface waves Rocks move sideways and up & down Slowest of the three types of waves Most destructive wave Surface Wave Animation

How are earthquakes measured? Seismograph: instrument that can detect, amplify, and record ground vibrations too small to be perceived by human beings Seisomogram: a graph showing the motion of the ground versus time Seismograph Animation Seismograph-ing to the beat Cali Seismogram Real Time

Travel-time curves Measures the time between P & S-waves (that hit a particular seismic station) Wave speed differs b/c of density & rigidity of Earth’s layers Tells you the distance of location from epicenter As the time between waves increases the distance from epicenter increases Time & Distance= Direct relationship!

Locating the Epicenter Use travel-time curve Ex. Difference between P & S waves=6.3 min What’s the distance from the epicenter? 4,000 km

Big Deal? What does that tell us… By looking at travel-times of seismic waves to different stations, we can generate a probability of epicenter location (scale distance on map) See circles around d1, d2 and d3? Where all 3 circles intersect tells us epicenter! Quake Movie Trailer

Determining Destruction Richter Scale measures magnitude (energy of largest seismic wave) on 1-10 scale looking at the wave’s largest amplitude Each magnitude is 10 times stronger than the previous magnitude Ex: magnitude 8 earthquake releases as much energy as detonating 6 million tons of TNT! Japan March 2011 Tsunami Photos Nat. Geo. Tsunami Animation Largest EQs Since 1900

Determining Destruction con’t Modified Mercalli Scale amount of shaking experienced at different locations (intensitydamage) Varies based on: overall magnitude how far you are from the fault that ruptured in the earthquake rock/ land texture or type (i.e. sand vs. concrete) More meaningful measure of severity to the nonscientist because intensity refers to the effects actually experienced at that place.

Mt. St. Helens Volcanoes

Zones of Volcanism Volcanism: all the processes associated with the release of magma, hot fluids, and gas Fueled by magma Rises to surface because less dense Called lava once at surface

Location of Volcanoes Mostly determined by plate boundaries NOT RANDOM! Mostly determined by plate boundaries Most at convergent and divergent boundaries 5% far from boundaries

Major Belt of Convergent Volcanoes Circum-Pacific Belt (Pacific Ring of Fire) Outlines the Pacific Plate Convergent volcanism: Plates colliding Continental subduction zones Characterized by explosive eruptions

Divergent Volcanism Formed where plates move apart New ocean floor is produced here Pillow lava forms at ocean ridges Characterized by non-explosive eruptions About 2/3 of Earth’s volcanoes occur at divergent boundaries Ex: Icelandic volcanoes uncharacteristically explosive due to hot spot

Bend in chain change in direction of plate movement! Hot Spots Unusually hot regions of Earth’s mantle where high-temperature plumes (columns) of magma rise to the surface Usually form far from plate boundaries Stationary – plate moves over spot Ex: Hawaiian Islands Bend in chain change in direction of plate movement!

Volcano Anatomy Conduit: tube-like structure that magma travels through to surface Vent: opening that lava comes out of Crater: bowl-shaped depression around the vent Usually less than 1 km (0.6 mi) in diameter

Types of Volcanoes 3 types: Appearance determined by: Type of material that forms volcano Type of eruptions 3 types: Shield Cinder cone Composite 1. 2. 3.

Shield Volcanoes Broad, gently sloping sides Non-explosive, quiet eruptions Made of layers of basaltic lava Largest type (width wise) Ex: Mauna Loa (Hawaii)

Cinder Cone Steep sides, cone shaped Mostly basaltic lava Explosive eruptions Smallest type (most less than 500 m or 0.3 mi high) Often on or near larger volcanoes Ex: Lassen Volcanic Park (California)

Composite Volcano Large, cone shaped, concave slopes Much larger than cinder cones Made of layers of rock (harden lava) from explosion and lava flows Violent eruptions (with periods of quiet ones) Ex: Mt, Augustine (Alaska), Mt. St. Helens (Washington)

Mt. Vesuvius, Italy Catastrophic eruption of A.D. 79 destroyed the cities of Pompeii and Herculaneum and killed at least 16,000 people Buried 10’ deep with lava & ash Thermal energy570 degrees F (300 degrees C) most died instantly of extreme heat, with many casualties shocked into a sort of instant rigor mortis. Most died instantly of extreme heat, with many casualties shocked into a sort of instant rigor mortis.