Our Ever Changing Earth Notes Part One

A Big Jigsaw Puzzle Tectonic Plates What Are They? Continental Drift – Whose Theory Started It? Alfred Wegener in 1912 What Are They? Earth’s Crust is called the Lithosphere, it is broken into smaller pieces – Tectonic plates Continental Drift – The Earth’s plates are moving, spreading out from each other

Continental Drift Wegener’s Reasoning Continents “Fit” Super Continent Pangaea Wegener’s Reasoning Continents “Fit” The continents piece together like a puzzle Fossils –Similar fossils have been found on either side of the Atlantic Ocean Glacial records There is evidence of glaciers in very warm climates Earth 100 Million Years From Now

Crustal Movement At first, no one believed him Plate Tectonics In the 1960’s, J. Tuzo Wilson said Continents aren’t moving, but the Earth’s crusts are. Plate Tectonics The Earth’s crust is in continuous motion due to convection currents of molten magma in the mantle.

The Tectonic Plates

Forming Mountains Mountains are formed in places called Converging zones Converging zone is an area where two plates are colliding. Since both plates are the same density, they both rise to form mountains.

Earthquakes At diverging plates, or similar extensional boundaries, earthquakes are shallow. Earthquakes in extensional environments tend to be smaller than magnitude 8. At transforms, earthquakes are shallow; mechanisms indicate strike-slip motion. Transforms tend to have earthquakes smaller than magnitude 8.5. At compressional boundaries the plates are converging. Compressional boundaries host Earth's largest quakes, with some events on subduction zones in Alaska and Chile having exceeded magnitude 9. There are three main plate tectonic environments: extensional, transform, and compressional. Plate boundaries in different localities are subject to different inter-plate stresses, producing these three types of earthquakes. Each type has its own special hazards.

Volcanoes A volcano begins as magma, melted rock inside the earth. At certain depths, the heat is so extreme that it partly melts the rock inside the earth. When the rock is melting, it produces gas which mixes together with the magma. The gas-filled magma slowly rises toward the surface of the earth because it is lighter than the solid surrounding rock. When the air in the magma rises, the magma rises with it and it blasts open the earth's crust. That's how a volcano is formed. Most volcanoes occur around the “Ring of Fire.” This can be seen on the upper right map. It surrounds the Pacific Ocean and is at the edge of several tectonic plates. There are three types of volcanoes: shield, composite, and cinder cone.

Shield Volcanoes Shield-Shield volcanoes are formed when a large amount of free-flowing lava spills slowly from a vent and spreads widely. The lava gradually builds up a low, broad, dome-shaped mountain. The Hawaiian Islands are of this type.

Composite Volcanoes Mount Saint Helens and many other volcanoes of the world, including Mount Rainier and Japan's Mount Fuji are solitary cones known as composite cones, or strato-volcanoes. Their slopes are made of layers of tephra(ash) and lava. Some of these volcanoes grow to greater than 3,000 meters above their bases. They are the most violent of the three types.

Cinder Cone Volcanoes Cinder cones are relatively small volcanoes composed of cinder ash. These volcanoes usually form steep-sided mounds with a small crater at the top. They commonly appear in clusters, sometimes mixed with more than a hundred neighboring cinder cones. They also occur on the slopes of other types of volcanoes, such as shield volcanoes.