1. EARTHQUAKES AND VOLCANOES Ms. Pollock Earth and Space Science Spring 2008

2. Earthquakes  Shaking and trembling that results from sudden movement of part of Earth’s crust  Most common cause faulting  Break in Earth’s crust along which rocks move  On sea floor can cause tsunamis  Ground rises and falls with seismic waves  Energy released during rock movements

4. Seismic Waves  Faults possible at Earth’s surface or deep within – most less than 74 km deep  Point where rocks break and move focus (underground point of focus)  Surface point directly above focus epicenter; source of most violent shaking  Earthquakes known as seismic waves  Tell about interior of Earth  Three main types

6. Seismic Waves  Primary (P) travel fastest; travel through solid, liquid, and gas; push-pull waves; cause rock particles to move back and forth  Secondary (S) travel through solids, but not liquids or gases; not recorded at all locations, since cannot pass through molten interior; cause rock particles to move side to side  Surface (L) waves slowest; travel from focus directly up to epicenter; most damaging, as they bend and twist Earth’s surface

7. Seismographs  Instrument that detects and measures seismic waves; weight attached to spring or wire  Not attached directly to Earth, so only moves when Earth quakes  Creates waves on paper  Seismologists determine strength of earthquake based on heights of wavy lines  Measured according to Richter scale – measure of energy released by earthquake  Any number above 6 very destructive  What determines the amount of damage done?

8. Predicting Earthquakes  Earthquakes studied in hope of accurate prediction in future  Useful prediction must be reliable and complete.  Prediction far enough in advance could make city planning easier.  San Francisco’s earthquake-proof buildings  Warning signals discovered by scientists  Change in speed of S and P waves  Small rise or fall of land near faults  Changes in water levels in wells

9. Formation of a Volcano  Magma deep within Earth under intense heat and pressure  Located in pockets called magma chambers  Magma constantly in motion through cracks or by melting rocks  Called lava at Earth’s surface  Can build up to form cone-shaped mountain  Location where lava reaches Earth’s surface called a volcano

11. Volcanic Eruptions  Different types of eruptions for different types of volcanoes  Some quiet, some very violent  Location of lava eruption called vent  Often multiple vents  Chemical composition of magma determined by analyzing mineral makeup of lava

12. Types of Lava  Dark with lot of water  Forms basalt  Rich in iron and magnesium  Light with little water  Rich in iron and magnesium with silica  Forms rhyolite  Intermediate composition  Composition between dark and light  Forms andesite  Large amounts of gases  Forms rock with many holes, such as pumice and scoria

14. Types of Lava and Eruptions  Dark lava – quiet flows  Runny and smooth  Islands of Hawaii and Iceland  Light lava – violent eruptions  Hardens in vents  Steam and new rocks build up beneath vents  Great pressure to cause explosions

15. Volcanic Eruptions  Rock fragments blown into air  Smallest particles volcanic dust; very fine  Particles size of rice grains volcanic ash; falls to Earth and forms small rocks  Large rock particles volcanic bombs; can be size of large boulders  Smaller bombs called cinders  Molten when leaving volcano; harden in air

16. Types of Volcanoes  Type of eruption affected by type of volcano  Some quiet and over large area  Some violent  Some combinations of quiet and violent

17. Cinder Cones  Made mostly of cinders and other rock particles  Formed from explosive eruption  Not high; narrow base with steep sides  Paricutin in Mexico

19. Shield Volcanoes  Quiet lava flows  Large area  Gently sloped, dome shaped mountain  Mauna Loa in Hawaii

21. Composite Volcanoes  Alternating layers of rock particles and lava  Beginning violent eruption with bombs, cinders, and ash from vent  Followed by quiet eruption with lava flow that covers rock particles  Large cone-shaped mountain result of many alternating eruptions  Mount Vesuvius in Italy and Mount Etna in Sicily

23. Volcanic Structure  Often crater at top – funnel-shaped pit or depression  If the crater becomes larger due to the collapse of walls, it is called a caldera.

24. Volcano and Earthquake Zones  Often volcano and earthquake zones in same areas of world  Sometimes one is the result of the other.  Most major occurrences in three zones of world.

25. Volcano and Earthquake Zones  Ring of Fire  Around edge of Pacific  New Zealand, the Philippines, Japan, Alaska, western coast of America affected  Near Mediterranean  Asia, India, Italy, Greece Turkey  Site of many volcanic eruptions  Iceland to middle Atlantic  Long ridge of under-ocean volcanic mountains  Formation of new parts of Earth’s crust

27. Continental Drift  Early 1900s, Alfred Wegener  Earth’s continents once joined in giant landmass, called Pangaea  Parts of supercontinent “drifted” to current positions  Theory called continental drift  50 years of study and gathering evidence before acceptance

29. Evidence From Fossils  Glossopteris – seed fern that grew in South Africa, Australia, and India 250 million years ago  Seeds to large to be carried over ocean to different continents  Mesosaurus – freshwater reptile found in South America and Africa  Only able to survive in shallow fresh water; could not survive to swim across Atlantic  When the landmass separated, some of the animals were left on each part.

30. Evidence From Rocks  Rock structure  Cape Mountains of South Africa folded mountains – formed by crumpling of Earth’s crust  End abruptly at Atlantic Ocean, matching rocks in Buenos Aires, Argentina  Glacial deposits  Rocks left behind by rock sheet; America, Africa, India, Australia, Antarctica similar  Mineral deposits  Salt, coal, limestone derived from coral reefs in unusual locations

32. Ocean Floor Spreading  Some scientists not accepting of continental drift until 1950s and 1960s  Better observations of ocean floor and new mapping techniques  Discovery of midocean ridges and rift valleys  Much volcanic and earthquake activity at midocean ridges  Lava erupting from rift valleys pushes ocean floor away as new seafloor forms  Deep-sea drilling  Rocks near midocean ridges found to be younger than rocks farther away from the ridge

33. Magnetic Stripes  Magnetic stripes in ocean-floor rocks  Magnetic minerals lined up in molten rock, becoming permanent magnets as the rocks harden  Discovered shifts in polarity of Earth  Pattern identical on both sides of midocean ridge – half moving in each direction

34. Plate Tectonics  Combination of continental drift and seafloor spreading  Lithosphere composed of seven major plates, named after surface features  Edges of continents not always boundaries; most boundaries on ocean floor  Three types of plate boundaries

35. Plate Boundaries  Divergent – plates moving apart; also called constructive; new material being made; midocean ridges  Convergent – plates coming together; also called destructive; material being subducted; trenches; violent reactions; Ring of Fire  Transform fault – usually found at right angles to midocean ridges; plates grinding and sliding; site of many earthquakes

36. Plate Motion  Believed that convection currents within Earth cause plate movements  Density of material altered due to extreme temperatures within Earth; hotter, less dense matter rises and pushes down cooler matter  Plates move on top of molten material  Oceanic crust more dense than continental crust; oceanic plates subducted beneath continental plates  Plate collisions cause folding with volcanoes, mountains, and trenches  Undersea volcanoes rising above surface of ocean create island arcs, like the Aleutians of Alaska

37. Past and Future Drifting  Plates moving different speeds and directions  Plates believed separate 510 million years ago, then formed Pangaea  Pangaea surrounded by single large ocean, Panthalassa  200 million years ago breaking of Pangaea  Current drift rate 1 to 5 cm per year