Volcanic earthquakes.
Upcoming SlideShare
Loading in...5
×

Like this? Share it with your network

Share

Volcanic earthquakes.

  • 772 views
Uploaded on

VOLCANIC EARTHQUAKES

VOLCANIC EARTHQUAKES

More in: Education , Technology
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads

Views

Total Views
772
On Slideshare
772
From Embeds
0
Number of Embeds
0

Actions

Shares
Downloads
4
Comments
0
Likes
0

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

  • 1. Introduction: The lowest part of the earth surface is formed of large pieces, called "tectonic plates". Those are floating over the boiling center of the earth, which is called "magma". As magma boils, it tends to move tectonic plates, that collide against each other. Obviously, those collisions take place at plates' edges. There, they generate "collision waves" that travel in all directions, but tend to dampen over distance. Thus, eartquakes tend to occur in the neighborhood of plates edges. On the other hand, magma tends to escape the center of earth at whatever leak it finds; those leaks are far more frequent along plates' edges rather than at the center of them. Hence, volcanoes (magma escape holes) tend to occur also along the tectonic plates' edges. http://answers.yahoo.com/question/index?qid=20071007090909AAVBfjH An earthquake can be caused two different ways, there is a volcanic eaerthquake and a tectonic earthquake. Tectonics earthquakes are much more common than volcanic earthquakes. Volcanic earthquakes are when the volcano produces acidic lava, which drys quickly, when it drys quickly it blocks the top of the volcano. So no more magma can escape. Presure starts to build up and eventually the acidic lava can no longer stand the presure. So the volcano is free to explode, the pressure is released so fast that an earthquake is caused. A volcanic earthquake is usually kept within 10-20 miles of the volcano. http://wiki.answers.com/Q/What_is_volcanic_earthquake Volcanically triggered earthquakes have the potential to cause cracks, ground deformation, and damage to manmade structures. They typically are much smaller than earthquakes caused by nonvolcanic sources. The largest felt volcanic earthquake in the Cascades was a magnitude 5.5 in 1981, under Mount St. Helens. http://www.pnsn.org/outreach/earthquakesources/volcanic Earthquakes Caused By Volcanoes Volcanic earthquakes are defined as the earthquakes which occur or are linked up with the volcanic activity.
  • 2. First, often before an eruption minor seismic activity increases in the vicinity of the volcano. Some kilometers below the volcanic vent, very hot viscous magma moves sluggishly under high steam pressure through a network of veins and arteries from one storage chamber to another. Due to this motion, various parts of the surrounding rock become hotter and more strained as the magma pushes them. These forces fracture the neighboring rocks, and the strain is relieved by small or moderate earthquakes. Second, sometimes fault rupture precedes the motion of magma and eruption of lava. The earthquake waves from the rupturing fault may shake up the molten material in the storage reservoir beneath the volcano. In a way, similar to the violent shaking of a bottle of soda pop, steam and gas that have previously dissolved in the magma begin to boil off and accelerate the escape of lava and gaseous material. This, in turn, would disturb the unstable equilibrium of the magma below the vent, and stimulate local volcanic earthquakes. Volcanic earthquakes are far less common than tectonic plate related ones. They are triggered by the explosive eruption of a volcano. When a volcano explodes the associated earthquake effects are usually confined to an area 16 to 32 km around its base. The volcanoes which are most likely to explode violently are those which produce acidic lava. Acidic lava cools and sets very quickly when it contacts air. This chokes the volcano’s vent and blocks the escape of pressure. The only way a blockage can be removed is by the pressure building up until it literally explodes the blockage outward. The volcano will explode in the direction of its weakest point, so it is not always upward. Extraordinary levels of pressure can produce an earthquake of considerable magnitude. The shock waves have been known to produce a series of tsunami in some instances. http://www.universetoday.com/82050/how-earthquakes-happen/ General principles of volcano seismology:  Seismic activity (earthquakes and tremors) always occurs as volcanoes awaken and prepare to erupt and are a very important link to eruptions. Some volcanoes normally have continuing low-level seismic activity, but an increase may signal a greater likelihood of an eruption. The types of earthquakes that occur and where they start and end are also key signs. Volcanic seismicity has three major forms: short-period earthquake, long-period
  • 3. earthquake, and harmonic tremor.  Short-period earthquakes are like normal fault-generated earthquakes. They are caused by the fracturing of brittle rock as magma forces its way upward. These short-period earthquakes signify the growth of a magma body near the surface and are known as 'A' waves. These type of seismic events are often also referred to as Volcano-Tectonic (or VT) events or earthquakes.  Long-period earthquakes are believed to indicate increased gas pressure in a volcano's plumbing system. They are similar to the clanging sometimes heard in a house's plumbing system, which is known as "water hammer". These oscillations are the equivalent of acoustic vibrations in a chamber, in the context of magma chambers within the volcanic dome and are known as 'B' waves. These are also known as resonance waves and long period resonance events. http://en.wikipedia.org/wiki/Prediction_of_volcanic_activity Types of Volcanic Earthquakes Two types of volcanically generated earthquakes are volcano-tectonic (VTs) earthquakes and long period earthquakes (LPs). Earthquakes produced by stress changes in solid rock due to the injection or withdrawal of magma (molton rock) are called volcano-tectonic earthquakes (Chouet, 1993). These earthquakes can cause land to subside and can produce large ground cracks. These earthquakes can occur as rock is moving to fill in spaces where magma is no longer present. Volcano-tectonic earthquakes don't indicate that the volcano will be erupting but can occur at anytime. Volcanic-tectonic earthquakes (VTs) are, simply put, caused by slip on a fault near a volcano. Volcanoes are often found in areas of crustal weakness and the mass of the volcano its self adds to the regional strain. Most VT earthquakes have nothing to do with the magmatic system of the volcano but occur in response to regional strain exerted in an area of weak faults. VTs can also be generated from changes of pressure under the volcano caused by the injection or removal of magma (molten rock) from the volcanic system. After the withdrawal of magma from a system, an empty space is left to be filled. The result is a collapse of surrounding rock to fill the void, also
  • 4. creating earthquakes. VT earthquakes can result in land deformation, collapse and/or ground failure but they are usually small and leave no trace on the surface. While these earthquakes may cause damage, they usually don't due to their small size which produces weak shaking. Occasional VTs or even in a significant swarm of dozens of events do not in themselves indicate an impending eruption. However, if a significant introduction of new magma from depth occurs in the system, both VTs and long period earthquakes are likely to be generated. The second category of volcanic earthquakes are long period earthquakes which are produced by the injection of magma into surrounding rock. These earthquakes are a result of pressure changes during the unsteady transport of the magma. When magma injection is sustained a lot of earthquakes are produced (Chouet, 1993). This type of activity indicates that a volcano is about to erupt. Scientists use seismographs to record the signal from these earthquakes. This signal is known as volcanic tremor. Volcanically-caused long period earthquakes are produced by vibrations generated by the movement of magma or other fluids within the volcano. Pressure within the system increases and the surrounding rock fails, creating small earthquakes. In 2004, Mt. St. Helens began dome building eruptions as magma was thrust upwards accompanied by long period earthquakes. These earthquakes are an indication of magmatic activity and may be a precursor to an eruption. When these earthquakes occur continuously the result is volcanic or harmonic tremor. Mount St. Helens exhibit these long period earthquakes months in advance of 1980's eruption. The volcanic tremor can be used to warn of an impending eruption allowing people living near the volcano can to be evacuated to safer areas. This method of prediction has been used successfully
  • 5. to predict the eruptions of Mount St. Helens in the 1980's and the 1991 eruption of Mt. Pinatubo in the Philippines. http://www.pnsn.org/outreach/earthquakesources/volcanic Why does volcanoes and earthquake happen mostly in the same place? Volcanoes usually form on plate boundaries. They form because the plates push upward against each other forming a small hole where magma can come out from the mantle. (the small hole is the where the magma comes out of on top of a volcano). Earthquakes usually are at faults lines and fault lines are near the plate boundaries. Since volcanoes and earthquakes happen usually at plate boundaries, they mostly happen in the same area. Volcanic eruptions and earthquakes take place in the same place as those regions have tectonic plates that are prone to movements. Sometimes, the plates move in different directions and at different speeds. They also crash, sideswipe each other or even pull apart. When this happens volcanic eruptions and earthquakes might occur. http://wiki.answers.com/Q/Why_does_volcanoes_and_earthquake_happen_mostly_in_the_s ame_place What is the differences between volcanic and tectonic earthquake? Volcanic earthquakes are caused by volcanic activities, or magma's activities to be precise. Tremors can be felt or recorded even if the volcano has not erupted yet. Increasing intensity and frequency of the tremors are usually used to predict when the volcano will erupt. Tectonic earthquake are caused by tectonic plates' movement relative to each other. These plates move in relation to one another at plate boundaries. Plate boundaries lock as the plates move past each other, creating frictional stress. When the frictional stress exceeds a critical value, called local strength, a sudden failure occurs, causing an earthquake. http://answers.yahoo.com/question/index?qid=20080227031654AAbBDiW Preventions from Volcanic Earthquakes: Earthquakes related to volcanic activity may produce hazards which include ground cracks,
  • 6. ground deformation, and damage to manmade structures. Earthquakes exhibiting volcanic tremor warn of an impending eruption so that people can be evacuated to areas of safety. The volcanic tremor signal has been used successfully to predict the 1980 eruptions Mount St. Helens and the 1991 eruption of Pinatubo. Volcano-tectonic earthquakes can cause damage to manmade structures and landsliding. To prevent damage from being done, structures should be built according to earthquake standards, building foundations should be constructed on firm ground and not unconsolidated material which may amplify earthquake intensity, and buildings should be constructed on stable slopes in areas of low hazard potential. http://www.geo.mtu.edu/volcanoes/hazards/primer/eq.html Conclusion: Earthquakes related to volcanic activity may produce hazards which include ground cracks, ground deformation, and damage to manmade structures. These earthquakes can cause land to subside and can produce large ground cracks. These earthquakes can occur as rock is moving to fill in spaces where magma is no longer present. Volcano-tectonic earthquakes don't indicate that the volcano will be erupting but can occur at anytime.
  • 7. ground deformation, and damage to manmade structures. Earthquakes exhibiting volcanic tremor warn of an impending eruption so that people can be evacuated to areas of safety. The volcanic tremor signal has been used successfully to predict the 1980 eruptions Mount St. Helens and the 1991 eruption of Pinatubo. Volcano-tectonic earthquakes can cause damage to manmade structures and landsliding. To prevent damage from being done, structures should be built according to earthquake standards, building foundations should be constructed on firm ground and not unconsolidated material which may amplify earthquake intensity, and buildings should be constructed on stable slopes in areas of low hazard potential. http://www.geo.mtu.edu/volcanoes/hazards/primer/eq.html Conclusion: Earthquakes related to volcanic activity may produce hazards which include ground cracks, ground deformation, and damage to manmade structures. These earthquakes can cause land to subside and can produce large ground cracks. These earthquakes can occur as rock is moving to fill in spaces where magma is no longer present. Volcano-tectonic earthquakes don't indicate that the volcano will be erupting but can occur at anytime.