Volcanoes are commonly conical hills or mountains built around a vent that connect with reservoirs of molten rock below the surface of the earth. Unlike other mountains, which are pushed up from below, volcanoes are built by surface accumulation of their eruptive products—layers of lava flows, ash flows, and ash. When pressure from gases within the molten rock becomes too great, gases drive the molten rock to the surface and an eruption occurs.
Volcanic eruptions can inject into the stratosphere tens of teragrams of chemically and microphysically active gases and solid aerosol particles that can affect the Earth’s radiative balance and climate and disturb the stratospheric chemical equilibrium.People have died from volcanic blasts. The most common cause of death from a volcano is suffocation. Volcanic eruptions can result in additional threats to health, such as floods, mudslides, power outages, drinking water contamination, and wildfires.
Volcanic eruptions can be placed into two general categories:those that are explosive, such as the 1980 eruption of Mount St. Helens, and those that are effusive, such as the gentle lava flows, fountains, and spatter cones common in Hawai'i. Many eruptions are explosive in nature.They produce fragmented rocks from erupting lava and surrounding parent rock.Non explosive eruptions are favored by low gas content and low viscosity magmas (basaltic to andesitic magmas).
Explosive eruptions are favored by high gas content and high viscosity (andesitic to rhyolitic magmas).
The major component of volcanic eruptions is magmatic material, which emerges as solid, lithic material or solidifies into large particles that are referred to as ash or tephra.Volcanic eruptions typically also emit gases, with water (H2O), nitrogen (N2) and carbon dioxide (CO2) being the most abundant.Most gases from a volcano quickly blow away. However, heavy gases such as carbon dioxide and hydrogen sulfide can collect in low-lying areas.
Tuesday, February 15, 2011
Sunday, February 13, 2011
How do earthquakes happen
How do earthquakes happen?Did you know that surface of the Earth is not one giant shell? It may look solid to us, but the Earth’s surface has cracks in it, and actually fits together like a puzzle. What happens when one of these gigantic puzzle pieces moves? An earthquake! Big earthquakes occur with movement of about a meter or two. Small earthquakes happen with movements of millimeters.Scientists cannot predict when an earthquake will take place, but they do understand why Earthquakes happen.In many ways, earthquakes are one of nature’s reminders that we are living on the thin outer crust of a planet whose interior is still cooling.The ground may feel strong and solid beneath our feet, but the tectonic plates can move without our noticing.
Most earthquakes occur at the boundaries where the plates of the Earth’s outer layer meet. In fact, the location of earthquakes and the kind of ruptures they produce help scientists define the plate boundaries. Most destructive quakes, however, are caused by dislocations of the crust. The crust may bend and then, when the stress exceeds the strength of the rocks, break and “snap” to a new position.
Earthquakes may occur in an area before,during, and after a volcanic eruption, but they are not the cause or result of volcanic activity; rather they are the result of the active forces connected with the volcanic eruption.Earthquakes are always happening somewhere.Large earthquakes occur about once a year. Smaller earthquakes, such as magnitude 2 earthquakes, occur several hundred times a day.
Measuring earthquakes
Used on the surface of the Earth, a seismograph can measure the seismic energy, or magnitude, of an earthquake. It does this by making lines on a page when the Earth vibrates. Lots of wavy lines mean the earthquake was large; fewer waves mean the quake was small.
Magnitudes are recorded on a scale called the Richter Scale.The Richter scale is the best-known scale for measuring the magnitude of earthquakes. The scale begins at 3.5, which is the magnitude assigned to earthquakes we can barely feel, to 8 or greater which are the highest magnitudes. Magnitude 8 earthquakes can destroy cities.
How can I protect myself in an earthquake?
Most earthquake-related injuries and deaths result from collapsing walls, flying glass, and falling objects caused by the ground shaking. It is extremely important for a person to move as little as possible to reach the place of safety he or she has identified, because most injuries occur when people try to move more than a few feet during the shaking.
Most earthquakes occur at the boundaries where the plates of the Earth’s outer layer meet. In fact, the location of earthquakes and the kind of ruptures they produce help scientists define the plate boundaries. Most destructive quakes, however, are caused by dislocations of the crust. The crust may bend and then, when the stress exceeds the strength of the rocks, break and “snap” to a new position.
Earthquakes may occur in an area before,during, and after a volcanic eruption, but they are not the cause or result of volcanic activity; rather they are the result of the active forces connected with the volcanic eruption.Earthquakes are always happening somewhere.Large earthquakes occur about once a year. Smaller earthquakes, such as magnitude 2 earthquakes, occur several hundred times a day.
Measuring earthquakes
Used on the surface of the Earth, a seismograph can measure the seismic energy, or magnitude, of an earthquake. It does this by making lines on a page when the Earth vibrates. Lots of wavy lines mean the earthquake was large; fewer waves mean the quake was small.
Magnitudes are recorded on a scale called the Richter Scale.The Richter scale is the best-known scale for measuring the magnitude of earthquakes. The scale begins at 3.5, which is the magnitude assigned to earthquakes we can barely feel, to 8 or greater which are the highest magnitudes. Magnitude 8 earthquakes can destroy cities.
How can I protect myself in an earthquake?
Most earthquake-related injuries and deaths result from collapsing walls, flying glass, and falling objects caused by the ground shaking. It is extremely important for a person to move as little as possible to reach the place of safety he or she has identified, because most injuries occur when people try to move more than a few feet during the shaking.
Tuesday, February 1, 2011
Facts about earthquakes
Earthquakes are short-term vibration of the Earth's crust caused by natural processes and tectonic movements in the lithosphere or artificially(caused by human activity).
Tectonic earthquakes(85%)
-resulting from tectonic movements in the lithosphere due to the sudden release of accumulated energy.Movement of molten mass in the asthenosphere causes the movement of tectonic plates where there is tension in different parts of the lithosphere.When they cross the border tension elastic substances liberated energy causes vibration of different parts of the lithosphere intensity.
Volcanic earthquakes(7%)
-Volcanic earthquakes are the result of the rapid movement of magma toward the surface, and their occurrence is mostly local and regional impacts.(often in very volcanically active areas tremors indicate the movement of magma toward the surface and points to a possible eruption)
Earthquakes collapse(3%)
-resulting from the collapse of cavities or voids in the earth's crust.
Blank spaces usually occur by dissolution of rock that are soluble in water (carbonates, evaporites). Their released energy is much smaller than the tectonic and volcanic earthquakes.Even if they have a limited impact can cause major damage.
Artificial earthquakes are caused by human activity:
-explosion,
-dive, or subsidence due to undermining and digging into the Earth's interior due to mining operations or other geotechnical engineering (mountain stroke),
-discharge of large reservoirs of water,
-pumping oil and water (shrug).
Seismograph-instrument for measuring and recording earthquake,
Seismometer-instrument to detect seismic waves,
Seismograms-records ground vibrations.
An earthquake usually starts with low blows, followed by the main shock,
followed by a weaker shock ..
Tectonic earthquakes(85%)
-resulting from tectonic movements in the lithosphere due to the sudden release of accumulated energy.Movement of molten mass in the asthenosphere causes the movement of tectonic plates where there is tension in different parts of the lithosphere.When they cross the border tension elastic substances liberated energy causes vibration of different parts of the lithosphere intensity.
Volcanic earthquakes(7%)
-Volcanic earthquakes are the result of the rapid movement of magma toward the surface, and their occurrence is mostly local and regional impacts.(often in very volcanically active areas tremors indicate the movement of magma toward the surface and points to a possible eruption)
Earthquakes collapse(3%)
-resulting from the collapse of cavities or voids in the earth's crust.
Blank spaces usually occur by dissolution of rock that are soluble in water (carbonates, evaporites). Their released energy is much smaller than the tectonic and volcanic earthquakes.Even if they have a limited impact can cause major damage.
Artificial earthquakes are caused by human activity:
-explosion,
-dive, or subsidence due to undermining and digging into the Earth's interior due to mining operations or other geotechnical engineering (mountain stroke),
-discharge of large reservoirs of water,
-pumping oil and water (shrug).
Seismograph-instrument for measuring and recording earthquake,
Seismometer-instrument to detect seismic waves,
Seismograms-records ground vibrations.
An earthquake usually starts with low blows, followed by the main shock,
followed by a weaker shock ..
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