Waves and Plate tectonics

1. Waves and Plate tectonics

2. Plate tectonics How did the theory come about? • The German meteorologist Alfred Wegener advocated "continental drift" in 1924. But people didn’t believe this idea. People started to think differently in the 1960’s due to evidence such as ; • Fossil records are similar between South America and Africa. • Some types of rocks match between South America and Africa. • There is a ridge in the mid-Atlantic. The current theory is ; • the crust is divided into rigid plates • the plates move (a few cm per year) • the driving force is convection currents in the mantle • at plate boundaries there are several possibilities • manufacture of new oceanic plate • plates slide along each other • continental plates crash into each other • oceanic plate is subducted under a continental plate

4. Types of plate boundaries • Divergent-A divergent plate movement occurs when two plates move away from each other. Magma from the mantle underneath the crust to rise up the surface to cool and solidify at the plate boundary. This divergent boundary is considered constructive since new crust is formed. • Convergent - When two plates move towards each other, they would collide. This is called a convergent plate movement. As the plates collide, some crust is destroyed due to the impact, therefore this convergent boundary is also called a destructive boundary. • Slip Strike - Fault rupture of the ground generates vibrations-or waves-in the rock that we fell as ground shaking. Faults are weaknesses in the rock and therefore earthquakes tend to occur over and over along the same faults. • Subduction zones - Subduction zones are the flip side of mid-ocean ridges in plate tectonics. They are destructive plate boundaries - sites where it is inferred that plates are taken back down into the atmosphere.

5. Volcanoes • Volcanoes occur when the Earth’s plates pull apart causing magma to rise to the surface. Volcanoes can also occur over hotspots and where one plate dives beneath another, forcing magma to rise to the surface. Plates diving under one another is known as subduction. • Volcanoes usually occur on the edges of plates, similar to where earthquakes occur. A lot of volcanoes occur in the area around the edge of the pacific ocean called the Pacific Ring Of Fire. Volcanoes can also occur in the middle of plates – hotspots. One such hotspot has formed the Hawaiian islands.

6. Shield volcanoes • Hawaii and Iceland are examples of places where volcanoes extrude huge quantities of basaltic lava that gradually build a wide mountain with a shield-like profile. Their lava flows are generally very hot and very fluid, contributing to long flows. The largest lava shield on Earth, Mauna Loa, rises over 9,000 m from the ocean floor, is 120 km in diameter and forms part of the Big Island of Hawaii, along with other shield volcanoes such as Mauna Kea and Kilauea. Olympus Mons is the largest shield volcano on Mars, and is the tallest known mountain in the solar system. Smaller versions of shield volcanoes include lava cones, and lava mounds. • Quiet eruptions spread out basaltic lava in flat layers. The build-up of these layers form a broad volcano with gently sloping sides called a shield volcano. Examples of shield volcanoes are the Hawaiian Islands

7. Cinder cones • Volcanic cones or cinder cones result from eruptions that throw out mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 m high. Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones.

8. Stratovolcanoes • Stratovolcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata that give rise to the name. Stratovolcanoes are also known as composite volcanoes. Classic examples include Mt. Fuji in Japan, Mount Mayon in the Philippines, and Mount Vesuvius and Stromboli in Italy.

9. Super Volcanoes • A super volcano is the popular term for a large volcano that usually has a large caldera and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulphur and ash erupted. They can be the most dangerous type of volcano. Examples include Yellowstone Caldera in Yellowstone National Park, Lake Taupo in New Zealand and Lake Toba in Sumatra, Indonesia. Supervolcanoes are hard to identify centuries later, given the enormous areas they cover. Large igneous provinces are also considered supervolcanoes because of the vast amount of basalt lava erupted.

10. Submarine Volcanoes • Submarine volcanoes are common features on the ocean floor. Some are active and, in shallow water, disclose their presence by blasting steam and rocky debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them prevents the explosive release of steam and gases, although they can be detected by hydrophones and discoloration of water because of volcanic gases. Even large submarine eruptions may not disturb the ocean surface. Because of the rapid cooling effect of water as compared to air, and increased buoyancy, submarine volcanoes often form rather steep pillars over their volcanic vents as compared to above-surface volcanoes. In due time, they may break the ocean surface as new islands. Pillow lava is a common eruptive product of submarine volcanoes.

11. Sub glacial volcanoes • Subglacial volcanoes develop underneath icecaps. They are made up of flat lava flows atop extensive pillow lavas and palagonite. When the icecap melts, the lavas on the top collapse leaving a flat-topped mountain. Then, the pillow lavas also collapse, giving an angle of 37.5 degrees. These volcanoes are also called table mountains, tuyas or (uncommonly) mobergs. Very good examples of this type of volcano can be seen in Iceland, however, there are also tuyas in British Columbia. The origin of the term comes from Tuya Butte, which is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analyzed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near the boundary with the Yukon Territory.