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Plate Tectonics in Action: Volcanoes, Mountain Building and Earthquakes!. Volcanoes. The term volcano comes from the name of the Roman god of fire, Vulcan . There are different types of volcanoes.
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Plate Tectonics in Action:Volcanoes, Mountain Building and Earthquakes!
Volcanoes The term volcano comes from the name of the Roman god of fire, Vulcan. There are different types of volcanoes. Eruptions vary from gentle flows (Hawaii and Iceland) to catastrophic explosions (Mount St. Helens, Mt. Pinatubo, Soufriere Hills). The majority of eruption never make the news because they occur beneath the ocean, unobserved.
Types of Volcanoes • There are two broad families of volcanoes: • Those formed by eruptions from a central vent. • Central-vent eruptions build mounds of the kind most people associate with volcanoes. • Those that erupt through a long fissure. • Fissure eruptions build plateaus. Typical Rift and Hot spot Eruptions Central vent Fissure
Cause of Volcanic Activity At subduction zones, the subducted plate is pulled downwards (slab pull) into the Earth's mantle—until it reaches a depth where high temperatures partially melt the rock. The resulting magma then rises along vertical fissures (cracks) and reaches the surface through a volcanic vent.
So why are some volcanos more "explosive" than others?#1 • The amount of gas inside magma is one of the things that determines how violent an eruption will be. • Under ground, gases remain under pressure in the magma, but when magma rises, the gases expand—increasing pressure! • Less gas = less violent eruptions because the small amount of gas easily escapes and less pressure is built up
The VISCOSITY, or thickness, of magma • Thick, sticky magma slows down the escape of gases and may also block a volcano’s main vent. • When the gases are finally released, they burst out! • These explosive eruptions are characterized by large clouds of flying rock particles, rather than lava flows. #2
When a volcano erupts from a central vent, dust and debris are produced that move at amazing speeds! • Pyroclastic flows are mixtures of hot, dry rock fragments and hot gases • They move away from the vent that erupted them at very high speeds #3: Pyroclastic Flow
Why are volcanoes so dangerous? • Dangers associated with volcanic eruptions go beyond the lava flows and debris and include: • Super-heated toxic gases and debris (pyroclastic flows) • Blast effects • Volcanic earthquakes • Landslides and lahars (mudflows), • Ash clouds or deposits
Mount St. Helens Eruption Spring 1980 Mt. St. Helens the day before its eruption in 1980. May 19, 1982 62 people died in thick ash and choking smoke and many more were injured. 400 square kilometres of forests were flattened and disappeared, and roads and bridges were demolished. Total economic losses were estimated at US $1.2 billion (in 1980 values).
What is an Earthquake? An earthquake is the shaking of the ground caused by a quick shift of rock along a fracture in the Earth, called a fault. Within seconds, an earthquake releases stress/energy that has slowly accumulated within the rock, sometimes over hundreds of years.... The origin of the earthquake along the fault is called the focus. The location on the surface of the earth directly above the focus is called the epicenter!
Let’s take a look.. Letterman’s take on it…
What Causes an Earthquake? When two plates collide, they sometimes get caught (or “stick”) and cannot slide past each other. The convection currents below them keep pushing the plates and, when they remain wedged, energy builds up… When the amount of energy built up exceeds the strength of the rock, the rocks break and the plates snap into a new position, releasing a huge amount of energy! This energy is released in the form of seismic waves, and an earthquake is started!
Types of Seismic Waves:P-(Primary)-waves P-waves (or primary waves) are formed by the alternate expansion and contraction of bedrock. They travel quickly relative to other waves and are the first waves measured after an earthquake. P-waves also have the ability to travel through solid, liquid, and gaseous materials. When some P-waves move from the ground to the lower atmosphere, the sound wave that is produced can sometimes be heard by humans and animals!
Types of Seismic Waves:S-(Secondary)-waves S-waves or secondary waves are produced by shear stresses and move the materials they pass through in a perpendicular (up and down or side to side) direction. These waves are slower than P-waves and can only move through solid materials (NOT LIQUIDS). Surface waves travel at or near the Earth's surface. These waves produce a rolling or swaying motion causing the Earth's surface to behave like waves on the ocean. The velocity of these waves is slower than body waves. Despite their slow speed, these waves are particularly destructive to human construction because they cause considerable ground movement.
Types ofSeismic Waves:L-waves L-waves (aka Surface waves) travel at or near the Earth's surface. These waves produce a rolling or swaying motion causing the Earth's surface to behave like waves on the ocean. The velocity of these waves is slower than s-waves. Despite their slow speed, these waves are particularly destructive to human construction because they cause the most ground movement.
Types of Waves on a Seismograph It is the time between the arrival of the P-waves and the S-waves that tells scientists how far they are from the epicenter of the earthquake!
Another hint in determining Earthquakes… • P waves can travel through liquid, though they will distort a little ...BUT • S waves CANNOT!
Measuring Earthquakes! There are two scales that are used to the strength of an earthquake: The Richter Scale measures the amount of ground movement using a seismometer This is a log scale… so every time the magnitude increases by one, the ground motion increases by 10 times! The Mercalli Scale measures the damage done This can be greatly different depending on where it happens, because of the land conditions, building materials, etc.!
Which do you think is more useful???
Did you Know….??? The largest recorded earthquake in the United States was a magnitude 9.2 that struck Prince William Sound, Alaska on Good Friday, March 28, 1964! The largest recorded earthquake in the world was a magnitude 9.5 in Chile on May 22, 1960!
Mountain Building! Mountains are primarily formed at convergent plate boundaries, where: An oceanic plate subducts under a continental plate, or Two continental plates collide and thrust upwards!
