Download Waves and Plate tectonics

Waves and Plate tectonics
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
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.
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.
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
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 shortlived 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.
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.
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.
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.
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 flattopped 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.