Tectonics Flashcards
(30 cards)
Timeline of Evidence Supporting Plate tectonics?
1915
Alfred Wegener came up with the theory that the continents once fitted together like the pieces of a jigsaw to form one super continent. He suggested that the plates are in constant movement. At first glance, it seems quite plausible that the continents did once must of fit together. he used research on fossils found across the world to show how animals must of once shared the same range for them to live in such different environments. h also had glacial evidence which backed up his claims, but he could not explain how this happened, so he was discredited.
WW1
-Sonar technology found ocean floor and it was not as flat a previously believed.
1919
-Seismic waves determine that the mantle is semi-plastic and material like liquid can flow through it. Arthur Holmes developed a theory that explains how the large landmasses on earth move convection in mantle.
1946
-Scientists make use of military sonar technology to map the ocean floor. they find the mid-ocean ridge, as well as mountains, volcanoes and deep ocean trenches.
1954
-The first World map of earthquakes.
1960
-Harry Hess and Robert Dietz proposed sea floor spreading theory of molten rock oozing and creating different sea floors.
1963
-Magnetic rock spreading away from the Atlantic Ocean proved Hess and Dietz theory.
1965
-Plate tectonics theory proposed by J.Tuzo Wilson.
1983
-Plate tectonics proven with the emergence of GPS.
What is the Crust and how is the oceanic crust different?
DESCRIBE
The crust is the outermost layer of the earth. It is composed of a mixture of igneous rocks. In addition there are some metamorphic and sedimentary rocks.
Oceanic crust is thinner in comparison to continental crust (about 8 kilometres thick) compared to 20-70 kilometres).
Because ocean crust forms at ocean ridges and is normally subducted within a few hundred million years,.
Continental crust is a mixture of igneous, metamorphic, and sedimentary rocks that is highly variable in age and composition.
What is the mantle?
DESCRIBE
The mantle below the crust makes up over 80% of the earth’s volume. It extends from the base of the crust to the outer core and is approximately 2800 kilometres in depth. The mantle consists of igneous rock, and has lots of iron and magnesium. The mantle is much hotter than the crust with the asthenosphere making up the majority of the mantle.
The mantle is split into the upper and lower mantle. As depth increases, the physical properties of the mantle change.
The upper mantle is the lithosphere and the lower mantle asthenosphere.
What is the core?
DESCRIBE
The core is a mixture of iron and nickel metals, with a little sulphur.
The inner core is a solid,whereas the outer core is a liquid.
The core is approximately 3490 kilometres in depth. Scientists using earthquake data about velocity of seismic waves were able to map out the various changes within the earth’s structure revealing the inner and outer core of the earth.
What are Plate Boundaries?
Plate Boundaries or plate margins describe the fault zones separating two distinct plates. There a three main types of plate boundary, namely, convergent, divergent and transform or conservative.
What are the types of Plate boundaries?
1) Convergent plate boundaries describe two plates that are moving into each other.
2) Divergent plate boundaries form when plates are moving apart.
3) Transform boundaries form as plates move alongside each other and in doing so create shear stress. These margins are associated with frequent earthquakes such as at the San Andreas Fault.
What are the 3 types of Convergent Plate Boundaries?
One, destructive oceanic-continental boundaries, where the younger and less dense oceanic crust is subducted under the older lighter continental crust.
Two, the destructive oceanic-oceanic boundary where one oceanic plate is subducted under another oceanic plate. Examples include these boundaries form oceanic island arcs like that of the Philippines.
Three, collision boundaries were a continental plate collides with a second continental plate. At this plate boundary fold mountains develop.
Examples include The Himalayas were formed in this way as India crashed into Eurasia around 50 million years ago.
What were the effects of the 2010 Haiti earthquake?
Primary
220,000 people were killed.
300,000 people were injured.
The main port was badly damaged.
Eight hospitals collapsed.
100,000 houses were destroyed and 200,000 were damaged.
1.3 million people became homeless.
Secondary
2 million people were left without food and water.
Frequent power cuts occurred.
Crime increased - looting became a problem and sexual violence escalated.
People moved into temporary shelters.
By November 2010 there were outbreaks of cholera.
Explain Liquefaction:
Soil liquefaction occurs when a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid.
It can turn the ground into quicksand.
Explain what a Lahar is?
A lahar is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley.
Define Pyroclastic Flow:
A dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing at great speed.
What is the difference of a shield volcano and a composite volcano?
A shield volcano has shield-like shape. They are typically very large in area but their cones have a smoother, lower profile than composite volcanoes. They are shaped this way because their lava flows are made of basaltic magma, which has a lower viscosity than the lava from composite volcanoes.
What is the fastest wave type?
Love waves
Define Hypocentre
The focus point within the ground where the strain energy of the earthquakes stored in the rocks are first released. The distance between this and the epicentre on the surface is called a focal point.
What is the Benioff Zone?
An area were seismic activity corresponds with the slab being thrust downwards in the subduction zone.
What are P-waves?
Primary waves are the fastest tectonic wave. They arrive first, but cause the least damage.
What are S-waves?
Secondary waves are the second fastest wave they shake the ground violently. This cause damage and liquefaction.
What are Love waves?
Love waves arrive last as they travel only across the surface, but they are the most destructive wave. They have a large amplitude and cause significant damage including fracturing the ground service.
What is a Jokulhlaup?
Devastating floods caused when volcanoes erupt benief glaciers and ice caps, creating huge volumes of meltwater. They are common in Iceland.
How are tsunamis created?
Tsunamis are generated when a sub-marine earthquake displaces the seabed vertically as a result of movement along the fault line at a subduction zone. The violent motion displaces a large volume of water in the ocean water column, which then moves outwards in all directions from the point of displacement.
What is the equation for determining a places risk?
Risk= Hazard x Vulnerability
——————————-
Capacity to Cope
What is a mega-disaster?
A disaster with unusually high impacts. Today that means millions of people affected and billions of dollars in damage over a wide area.
What are the 3 main impacts of tectonic hazards?
1) Social: Deaths, injury and wider health impacts, including psychological issues.
2) Economic: The loss of property, businesses, infrastructure and opportunity.
3) Environmental: Damage or destruction of physical systems, especially ecosystems.
What are Hazard profiles?
A hazard profile is a description and analysis of a specific type of local hazard. It is performed for each natural hazard and based off of criteria such as frequency, duration, and speed of onset.
