Mountain ranges provide us with continuous evidence that the Earth’s surface is constantly changing shape. › These changes result from deformation, or the bending, tilting, and breaking of Earth’s crust. Happens when the lithosphere thickens or thins out.
Vertical movement of the lithosphere depends on two opposing forces: › Gravitational Force Weight of the lithosphere pressing down on the asthenosphere. › Buoyant Force The asthenosphere pressing up on the lithosphere. A condition of gravitational and buoyant equilibrium between Earth’s lithosphere and asthenosphere is called isostasy.
As Earth’s lithosphere moves, the rock in the crust is squeezes, stretched, and twisted. › The amount of force per unit area that acts on a rock is called stress. 3 types include: 1. Compression 2. Tension 3. Shear Stress
The type of stress that squeezes and shortens a body of rock. Common along convergent plate boundaries where tectonic plates collide with one another.
The type of stress that stretches and pulls a body of rock apart. Common along divergent plate boundaries where tectonic plates are being pulled apart.
The type of stress distorting a body of rock by pushing parts of the body in opposite directions. Common along transform plate boundaries where tectonic plates slide horizontally past one another.
A bend in rock layers resulting from stress is known as a fold. › The sloping sides of a fold are called limbs. › The limbs meet at the bend in the rock layers, which is called the hinge. › If the fold’s structure is such that a plane could slice the fold into two symmetrical halves, the fold is symmetrical and the plane is called the axial plane.
Downward trough-like folds are called synclines.
Folds where rock layers are folded so both ends of the fold are horizontal are called monoclines.
Recall, a fault is a break in the Earth’s crust along which blocks of the crust slide relative to one another.
A normal fault occurs when the hanging wall moves down relative to the footwall. › Results from tension.
A reverse fault occurs when the hanging wall moves up relative to the footwall. › Results from compression.
Faults that occur when opposing forces cause rock to break and move horizontally are called strike-slip faults. › Results from shear stress.
An earthquake is the movement or trembling of the ground caused by a sudden release of energy when rocks along a fault move. › Each year, over 30,000 earthquakes occur worldwide strong enough to be felt. › However, only about 100 major earthquakes take place each year.
Earthquakes are a result of elastic rebound, which is the sudden return of elastically deformed rock to its un-deformed shape.
The location within the Earth along a fault at which the first motion of an earthquake occurs is called the focus. › By the time vibrations from an earthquake having a deeper foci reach the surface, much of their energy has dissipated. › Therefore, earthquakes causing the most damage tend to have shallow foci. The point on Earth’s surface directly above the focus is called the epicenter.
As rocks along a fault slip into new positions, the rocks release energy in the form of vibrations called seismic waves. Two main types of seismic waves: › Body – seismic waves traveling through the body of a medium (fastest-moving seismic wave category). P waves S waves › Surface – seismic waves traveling along the surface of a body rather than through the middle of it (slowest- moving seismic wave category; most destructive). Rayleigh waves Love waves
Body waves traveling through solids and liquids are called P waves. “Primary” waves “Pressure” waves Fastest seismic wave. › Avg. speed in crust = 6.1 km/s Particles of rock move in a back-and-forth direction.
Body waves traveling through only solids are called S waves. “Secondary” Waves “Shear” Waves Second fastest seismic wave. › Avg. speed in crust = 4.1 km/s Particles of rock move in a side-to-side direction.
Rayleigh waves are surface waves causing the ground to move with an elliptical, rolling motion. Love waves are surface waves causing the ground to move with a side to side motion perpendicular to the direction of the traveling wave.
Vibrations in the ground can be detected and recorded using an instrument known as a seismograph. › First seismograph by Chinese astronomer, Chan Heng. Each of the 8 dragons had bronze ball in its mouth fell with tremor. A tracing of an earthquake motion recorded by a seismograph is called a seismogram. A person who studies earthquakes is a seismologist and the study of earthquakes is called seismology.
To determine the distance to an epicenter, scientists analyze the arrival times of the P waves and the S waves. › The longer the lag time between the arrival of the waves, the farther away the earthquake occurred. Scientists use computers to calculate how far an earthquake is from a given seismograph station. What is the lag time for the earthquake recorded on the seismogram to the left?
A measure of the strength of an earthquake is called magnitude. › Determined by measuring the amount of ground motion caused by an earthquake. The Richter Scale was used throughout the 20th century to study magnitude. › It is a logarithmic scale, meaning the numbers on the scale measure factors of 10. Therefore, an earthquake measuring a 4.0 on the Richter Scale is 10 times larger than one measuring at a 3.0.
Scientists now prefer to measure the magnitude of earthquakes with the Moment Magnitude Scale. › It is a measurement of earthquake strength based on the following: Size of the area of the fault. Average distance the fault blocks move. Rigidity of the rocks in the fault zone. Although this scale gives similar values as the Richter Scale, this one is more accurate.
Before the development of the magnitude scales, the size of an earthquake was determined based on the earthquake’s effects on the area. A measure of the effects of an earthquake is called the intensity. The Modified Mercalli Scale expressed intensity in Roman Numerals I to XII (highest- total destruction).
Any activity including the movement of magma onto Earth’s surface is called volcanism. › Molten rock beneath Earth’s surface is called magma. › Once it erupts onto the surface, it is termed lava. The vent in Earth’s surface through which magma and gases are expelled is called a volcano. › Most active volcanoes occur in zones near both convergent and divergent plate boundaries.
Many volcanoes are located along subduction zones, where one tectonic plate moves under the other. › As the subducting plate gets deeper into the asthenosphere, the rock melts and forms magma. › The magma rises through the lithosphere (less dense) and erupts on Earth’s surface.
Not all volcanoes develop along plate boundaries. › Areas of volcanism within the interiors of the lithosphere are called hot spots. Most form where columns of solid, hot material from the deep mantle, called mantle plumes, rise and reach the lithosphere. The plume will spread out and magma will break through the Earth’s crust resulting in the formation of a hot spot volcano (HI Island formation).
Mafic (dark-colored; rich in Fe and Mg) magmas are common with non-explosive volcanic eruptions since gases can easily escape generally quiet. Most common type of eruption. Produce relatively calm flows of lava, but can produce huge amounts of it.
Felsic (light-colored; high Si content) magmas are common with explosive eruptions since large amounts of gases are trapped inside. › Effects can be incredibly destructive. During explosive eruptions, clouds of hot debris, ash, and gas shoot rapidly out from a volcanic vent. › Fragments of rock forming during a volcanic eruption is called pyroclastic material.
The viscosity of magma, or its resistance to flow, affects the force with which a particular volcano will erupt. › A glass of milk has LOW viscosity, flowing more quickly. Common with mafic magmas. › A milkshake has HIGH viscosity, flowing slowly. Common with felsic magmas. Four main types of lava: Pahoehoe Aa Blocky Lava Pillow Lava
Lava flowing similar to wax dripping from a candle (LOW viscosity). As it cools, it forms a smooth, rope-like texture.
Lava flowing quickly (LOW viscosity), forming a brittle crust. The crust is torn into jagged pieces as molten lava continues to flow underneath.
Higher Si content than Aa; cooler, stiff lava usually oozing and flowing slowly (HIGH viscosity) from a volcano after an explosion. Cooled lava eventually breaks into blocks.
Forms when lava erupts underwater. This lava flows quickly (LOW viscosity) and has rounded lumps resembling pillows.
Magma rises to the surface, like an air bubble in a honey jar. › This happens because the magma is less dense than surrounding rock. Three main types of volcanoes: › Shield Volcanoes › Cinder Cone Volcanoes › Composite Volcanoes
When the magma chamber below a volcano empties, the volcanic cone may collapse and leave a large, basin- shaped depression called a caldera. Calderas may later fill with water to form lakes. › Common example: Crater Lake, OR
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