Plastic deformation
When stress is applied to a rock, the rock can deform in one of three ways:First, the rock deforms elastically. If the stress is removed, the rock springs back toits original size and shape (releasing the stored energy).Under other conditions, when its elastic limit is exceeded, a rock continues to deform like putty. This behavior is called plastic deformation. A rock that has deformed plastically keeps its new shape when the stress is released, and consequently does not release the energy used to deform it.
Fault
However, every rock has a limit beyond which it cannot deform elastically. Under certain conditions, an elastically deformed rock may suddenly fracture (creating a fault). The fracture releases the elastic energy, and the rock springs back to its original shape. When large masses of rock in the Earth's crust deform and then fracture, the resultant rapid motion creates vibrations that travel through the Earth and are felt as an earthquake.
Earthquake
An earthquake is a sudden motion or trembling of the Earth caused by an abrupt release of energy that is stored in the rocks.
Seismic waves
Waves transmit energy from one point to another. Waves that travel through rock are called seismic waves. Earthquakes produce seismic waves.
Focus / epicenter
The initial point, where the abrupt movement creates an earthquake, typically lie below the surface at a point called the focus. The point on the Earth's surface directly above the focus is the epicenter.Two main types of body waves travel through the Earth's interior:P wave: compression elastic wave that causes alternate compression and expansion of the rock. P waves are called primary waves because they move so fast (4-7 km per sec) that they are the first seismic waves that reach an observer.S wave: shear wave are termed secondary waves because they move more slowly (3-4 km per sec) that P waves.
Body waves: P waves and S waves
An earthquake produces several different types of seismic waves. Body waves travel through Earth's interior and carry some of the energy from the focus to the surface.
Surface waves
Surface waves then radiate from the epicenter along the Earth's surface.Surface WavesDuring an earthquake, surface waves move the Earth's surface up and down and from side to side.
Seismograph
A seismograph records ground motion during an earthquake. In early versions of seismography the pen draws a straight line across the rotating drum when the ground is stationary. When the ground rises abruptly during an earthquake, it carries the drum up with it. But the spring stretches so the weight and pen hardly move. Therefore the pen marks a line lower on the drum. Conversely, when the ground sinks, the pen marks a line higher on the drum. During an earthquake the pen traces a jagged line as the drum rises and falls.
Locating epicenter
A time-travel curve. With this graph you can calculate the distance from a seismic station to the epicenter of an earthquake. In the example shown, a three-minute delay between the first arrivals of P waves and S waves corresponds to an earthquake with an epicenter 1900 kilometers from the seismic station.
Processes that function to melt asthenosphere for magma formation: Spreading center (divergent plates) Mantle plumes Subduction zones
Three processes function to melt the asthenosphere to form magma: increasing temperature, decreasing pressure, and addition of water.Three processes melt the asthenosphere to form magma at a subduction zone:(1) Steam rises from wet oceanic crust on top of the subducting plate;(2) circulation in the asthenosphere decreases pressure on hot mantle rock;(3) friction heats rocks in the subduction zone.Magma forms abundantly in three tectonic environments: spreading centers (divergent plates)mantle plumessubduction zones
Pressure release melting
Pressure-release melting produces magma beneath a spreading center, where hot asthenosphere rises to fill the gap left by the two separating tectonic plates.
Mantle plume / hotspot
Pressure-release melting produces magma in a rising mantle plume (small rising column of hot, plastic mantle rock). The magma rises to form a volcanic hot spot.
Ring of Fire
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Pluton (batholith / stock)
In most cases, magma solidifies within the Earth's crust to form a large mass of granite called a pluton.A pluton is any intrusive igneous rock. A batholith is a pluton with more than 100 square kilometers exposed at the Earth's surface. A stock is similar to a batholith but has a smaller surface area.
Dike / sill
A large magma body may crystallize within the crust to form a pluton. Some of the magma may rise to the surface to form volcanoes and lava flows; some intrudes country rock to form dikes (tabular, or sheetlike, intrusive rock that forms when magma oozes into a fracture) and sills (sheetlike rock parallel to the layering).
Pahoehoe and aa lava
Lava with low viscosity may continue to flow as it cools and stiffens, forming smooth, glassy-surfaced, wrinkled, or "ropy" ridges. This type of lava is called pahoehoe.If the viscosity of lava is higher, the surface may partially solidify as it flows. The solid crust breaks up as the deeper molten lava continues to move, forming aa lava with a jagged, rubbled, broken surface. As the lava cools, escaping gases such as water and carbon dioxide form bubbles in the lava.
volcanic ash / cindersFlood basaltVolcano / vent / crater
If a volcano erupts explosively, it may eject both liquid magma and fragments called tephra.The smallest particles, called volcanic ash, consist of tiny fragments of glass that formed when liquid magma exploded into the air. Cinders are volcanic fragments that vary in size from 2 to 64 mm. Fragments greater than 64 mm are termed volcanic blocks.In some cases, fissures extend for tens or hundreds of kilometers and pour thousands of cubic kilometers of lava onto the Earth's surface. A fissure eruption of this type creates a flood basalt, which covers the landscape like a flood. When many such fissure eruptions occur in rapid succession it creates a lava plateau (basalt plateau) covering thousands of square kilometers. Volcanoes differ widely in shape, structure, and size. Lava and rock fragments commonly erupt from an opening called a vent located in a crater, a bowl-like depression at the summit of the volcano.
Shield volcano
Fluid basaltic magma often builds a gently sloping mountain called a shield volcano.
Cinder cone
A cinder cone is a small volcano composed of pyroclastic fragments. A cinder cone forms when large amounts of gas accumulates in rising magma
Composite cone
composite cone consists of alternating layers of lava and loose pyroclastic material. The cone is formed over a long period of time from alternating lava flows and pyroclastic eruptions. The hard lava covers the loose pyroclastic material and protects it from erosion.
Caldera
When granitic magma rises to within a few kilometers of the Earth's surface, it stretches and fractures overlying rock. Gas separates from the magma and rises to the upper part of the magma body.(B) The gas- rich magma explodes through fractures, rising as a vertical column of hot ash, rock fragments, and gas. (C) When the gas is used up, the column collapses and spreads outward as a high-speed ash flow.(D) Because so much material has erupted from the top of the magma chamber, the roof collapses to form a caldera.