Tectonic Processes Q. Which of the four spheres are we going to examine?
Lithosphere • brittle outer layer of the Earth that includes the crust and uppermost mantle • six major and several minor tectonic plates that move around on the softer asthenosphere. (The relatively plastic layer of the upper mantle on which the tectonic plates move. Approximately 200 km [124 miles] thick • Oceanic plates thinner (at points less than 50 km thick) • Continental plates denser/thicker (more than 120 km thick in places like the Himalayas) • Plates ‘float’ because of isostasy. (gravitational equilibrium between the lithosphere and the asthenosphere)
What causes the plates to move? Convection! Cool picture
Lithosphere(Plate Tectonics and Earthquakes) • Types of Plate Boundaries: • convergent (compression) - can form mountain belts (fold mountains like the Himalyas), off shore trenches and subduction zones (volcanoes often occur - Mt. Edgecomb, Mt. St. Helen’s) • Compression folds: anticline, syncline • Divergent (tension) - creation of new crust as material wells up from below separating plates (ridges like the Mid-Atlantic Ridge, rift valleys like the Red Sea) • Transform (transform and strike -slip) - plates slip against each other (San Andreas Fault) • Draw with me! Exam? rift valleys, trenches, island arcs, mid-ocean ridges, fold mountains - Take down this website! http://earthquake.usgs.gov/learning/
Lithosphere (The Rock Cycle) Types of Rock Igneous Rock Igneous rock are formed from magma that has cooled and solidified: A. within the Earth's crust Intrusiveor B. on the Earth's surface Extrusive Magma that solidifies within the Earth's crust cools slowly and result in coarse-grained (large crystal) rock; for example, granite. Magma that solidify at or near the Earth's surface cools rapidly and result in fine-grained (small or no crystal) rock; for example, basalt and obsidian. Sedimentary Rock Rock composed of sediment, ie, solid particles and dissolved minerals. Examples include rocks that form from sand or mud in riverbeds or on the sea bottom. Thinks layers. For example, sandstone, limestone) Metamorphic Rock Due to heat and pressure deep in the Earth’s crust, rocks change their original mineral compositions and textures. Metamorphic rocks can form from igneous, sedimentary or older metamorphic rocks. (For example, slate, marble)
Earthquakes are an observable characteristic of plate tectonics Q. How do we find the epicenter (point on earth directly above hypocenter) of an earthquake? A. velocity = distance divided by time
Lithosphere(Plate Tectonics and Earthquakes) • P-waves are Primary or Compressional Waves. Faster waves that have speeds of 5 km/s at the top of the crust, 8 km/s at the top of the mantle, and 14 km/s at the bottom of the mantle. They can travel through liquids and so can pass through Earth's liquid outer core. • S-waves are Shear or Transverse waves. Slower than P-waves, they cannot travel through liquids and do not pass through the Earth's core. • Note: Waves start at the hypocenter. Earthquakes send out P & S-waves. Aftershocks are smaller quakes after the original and stronger quake. If the aftershock is greater than the original Earthquake, the original earthquake is a foreshock.
Richter Scale (measuring earthquakes) Magnitude Earthquake Effects Estimated Number Each Year 2.5 or less Usually not felt, but can be recorded. 900,000 2.5 to 5.4 Often felt, but only causes minor damage. 30,000 5.5 to 6.0 Slight damage to buildings and other structures. 500 6.1 to 6.9 May cause a lot of damage in populated areas. 100 7.0 to 7.9 Major earthquake. Serious damage. 20 8.0 or greater Great earthquake. Can totally destroy communities near the epicenter. One every 5 to 10 years The Richter magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the Richter scale, the amplitude of the ground motion recorded by a seismograph goes up ten times. A magnitude 1 seismic wave releases as much energy as blowing up 6 ounces of TNT. A magnitude 8 earthquake releases as much energy as detonating 6 million tons of TNT.
Exam ? epicenter, tremors, graben and horst Hazards of Earthquakes 1. Liquefaction: soil becomes a viscous fluid 2. Mass Wasting: The downward movement of earth materials in response to gravity. (Can be triggered by a quake, avalanche) 3. Tsunami: An ocean wave generated by a submarine earthquake, volcano or landslide. (Also known as a seismic seawave, and incorrectly as a tidal wave).
Lithosphere (Volcanoes) There are 6 types of volcanoes (created at plate boundaries and hotspots) the 3 most common are: Shield • runny, low viscosity lava • sides slope at 15 degrees or less • (resembles a Roman shield lying on the ground, hence its name) characterized by relatively quiet eruptions with lava flows • relatively little explosive activity • GOOD WEBSITE Mauna Loa, Hawaii
Composite (about 60% of the Earth's volcanoes ) • large (1 - 10 km across) • layered structure, consisting of alternating layers of lava and pyroclastic material • Examples: Mt. Vesuvius, Cascade Range volcanoes such as Mt. St. Helens and Mt. Rainier Mt. St. Helen’s
Cinder • relatively small (less than 300 m or 1000 ft high) • relatively steep slopes (30 - 40 degrees) • made of pyroclastic material Puu Puai,, Kilauea, Hawaii And what, you ask, is pyroclastic material?
Exam? Terms you need to know and identify: Intrusive Features- Igneous rock that crystallizes below the ground Dyke - vertical wall-like discordant features formed as a result of magma being injected into the fractures of rocks. Tthey cut through existing layers of rocks. Sill - a flat (usually horizontal, concordant) mass of igneous rock between two layers of rock Laccolith - Formed when magma is injected between layers of rock (concordant). The pressure of the magma being injected overlying strata upward; hence Batholith - an extremely large mass of igneous rock. May be exposed due to erosion. Typically discordant, but may be partly concordant. Draw with me!
Extrusive Feature - Igneous rock that crystallizes at the surface. Columnar Jointing - a flat (usually horizontal) mass of igneous rock between two layers of older sedimentary rock, often six-sided. Hey, has anyone been to Miles Canyon? Caldera - Large volcanic crater created by explosion or internal collapse of a volcanic cone
biosphere (life, including humanity, fossils, and evolution): • includes all life on Earth, past as well as present • Q. But what does the biosphere have to do with Volcanoes?
Volcanic effects on the atmosphere and biosphere On Kilauea Volcano in Hawaii, upwind from the volcano is a tropical rain forest, and downwind from the volcano is the barren Ka'u Desert where the vog and acidic rain have killed the plants. Volcanic Hazards Google videos of volcanoes
Pyroclastic Do you want to see the pyroclastic flow of Mt. St. Helen’s? Pyroclastic: A pyroclastic flow is an avalanche of pyroclastic materials (broken rocks, pumice, and ash) and hot gases that erupts from within a volcano. (Can travel up to 100 miles per hour and reach 500 degrees C. Throw water into the mix and you have a lahar. Riddle me this batkids, Can a pyroclastic flow/ Lahar be dangerous to life and property?
Benefits of Volcanoes • Volcanic rocks decompose very rapidly and form soils that are rich in the nutrients used by plants; in fact, soils derived from volcanic rocks are among the most fertile in the world. (Ironically, it's this connection with agriculture that induces about 10 percent of the world's population to live in the shadow of active volcanoes.) • Hot springs are very common in volcanic areas. • In many parts of the world, this geo-thermal (volcanic) heat is collected and used to generate electricity or directly heat buildings. (The capital of Iceland, a city of over 100,000 people, is heated almost exclusively using geothermal energy.) • Creation of landmass (Anyone want to go to Hawaii? • Mafic and Ultramafic Minerals such as gold and diamonds (Think NWT Diamonds - Kimberlite Pipes - extinct volcanoes • Tourism (Costa Rica, Hawaii)