Saturday, March 26, 2011

Shield volcanoes

Shield volcanoes are tall and broad with flat, rounded shapes. They have low slopes and almost always have large craters at their summits.Shield volcanoes can be very big. An example is Mt. Kilauea (in Hawaii, USA).
Shield volcanoes are built almost entirely of fluid lava flow. Flow after flow pours out in all directions from a central summit vent, which builds a broad, gently sloping cone - much like a warrior's shield or a plateau.As the lava cools, it dips down in the center leaving sloped sides, like a bowl or a shield.These volcanoes do not explode the way composite volcanoes do; instead, lava just flows out of them.Their eruptions consist of hot, flowing basaltic lava that travels a long way before it solidifies.
Many volcanoes that form above hot spots are shield volcanoes.
Shield volcanoes have much smaller eruptions producing less ash. However they pour out a lot more lava over a long period of time.
Olympus Mons is, a giant shield volcano on Mars. It is believed to be the largest volcano in the solar system.
Mauna Loa, a shield volcano on the "big" island of Hawaii, is the largest single mountain in the world, rising over 30,000 feet above the ocean floor and reaching almost 100 miles across at its base.
However some volcanoes like Mauna Loa stay active and erupt much more often.The Hawaiian volcano of Kilauea has thrown lava nearly 2,000 feet into the air.

Friday, March 25, 2011

Composite volcanoes

Composite volcanoes have a principal conduit system through which magma from a reservoir deep in the Earth's crust rises to the surface repeatedly to cause eruptions.Composite volcanoes, sometimes called stratovolcanoes, tend to erupt explosively because of the silica-based nature of magmas associated with these volcanoes.

Composite volcanoes often form the largest and tallest volcanoes. They are the most explosive and dangerous of the types of volcanoes.
Most of the tall volcanoes, like Mount St. Helens and Mount Rainier in Washington and Mount Fuji in Japan are composite volcanoes. These volcanoes usually have a big explosion when they erupt, and in-between eruptions you might not even be able to tell they are volcanoes, because they are very quiet and look just like other
mountains.
Shape is largely a function of slope angle; at the one
extreme are very shallow slopes that characterize shields, and on the other are the steeper slopes that characterize cones and domes. Among the smaller edifices are cinder cones and domes, which are typically monogenetic (formed from a single eruption episode).

Compared with caldera systems, composite volcanoes erupt smaller volumes more frequently and less explosively, which likely inhibits the long-term extreme differentiation, which typifies caldera-forming magmas.Young stratovolcanoes are typically steep sided and symmetrically cone shaped. There are several active stratovolcanoes in North America. Since 1980 Mount Saint Helens in Washington has become the most familiar.dimension built of alternating layers of lava flow, volcanic ash and cinders.

Famous composite volcanoes include Mount Fuji in Japan, Mount Shasta and Mount Lassen in California, Mount St. Helens and Mount Rainier in
Washington State, Mount Hood in Oregon, and Mount Etna in Italy.
Composite volcanoes will rise as much as 8,000 feet above their base. Most composite volcanoes have a crater at the summit, which contains a central vent or a clustered group of vents.Most volcanoes on Earth are of this type. Stratovolcanoes kill more people than any other type of volcanoes - this is because of their abundance on Earth and their powerful mudflows.

Wednesday, March 23, 2011

Active volcanoes

Active volcanoes are those that are currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions.Regularly active volcano ejected lava, ash, smoke and other substances. With a very active volcano this happens almost constantly. In the other between the eruption extended weeks or months.
While there is evidence of volcanic activity in the past, a lot of volcanoes are active today. They’re bubbling with lava, spewing ash and triggering earthquakes as you sit in class.Explosive eruptions can shoot columns of gases and rock fragments tens of miles into the atmosphere, spreading ash hundreds of miles downwind.
While some of the volcanoes are dormant for hundreds of years, others who were believed to be extinct, become active again, as happened 1973rd with Helgafelom (Hajmej, Iceland).

Alaska is home to 41 historically active volcanoes stretching across the entire southern portion of the State from the Wrangell Mountains to the far Western Aleutians. An average of 1-2 eruptions per year occur in Alaska.

Mount Etna, the largest active volcano in Europe, reaching 3,350 m and covering a surface of about 1,260 km2, started its activity at about 600 ka, after the end of  Upper Pliocene to Pleistocene subaqueous and subaerial eruptions at the northwestern edge of the Iblean Plateau. Mt.
The New Zealand area is characterised by both a high density of active volcanoes and a high frequency of eruptions.

The largest volcanic eruption of the 20th century occurred at Novarupta Volcano in June 1912. It started by generating an ash cloud that grew to thousands of miles wide during the three-day event.
Some volcanoes expel gas and burning lava in the terrifying outbursts. Others have explosive eruptions and expel clouds of ash and gas.Volcanoes are evidence that the Earth is restless, especially within the crust and upper mantle.

If you live near an active or dormant volcano, you should be prepared to evacuate at a moment’s notice, as eruptions are not always predictable.Volcanoes can be incredibly destructive to buildings and dangerous to your family. In addition to the direct hazards, an eruption can be accompanied by landslides, mudflows, flash floods, earthquakes and tsunamis.

Tuesday, March 22, 2011

Atacama desert facts

Facts about the Atacama are very interesting. The Atacama Desert is between the central Andes and Pacific Ocean in northern Chile. Located in northern Chile and extreme southern Peru, the Atacama Desert is located is perhaps the most unique physiographic location on earth. The Atacama Desert is also known as the Sechura Desert.

 It is driest desert in the world. The Atacama Desert lies between two mountain ranges on the west coast of South America, the Coastal Cordillera and the Andean Cordillera. The Coastal Cordillera ranges in elevation from 500 to 3000 meters, and the Andean Cordillera ranges in elevation from 5000 to 6000 meters.Unlike other deserts, such as the Sahara in Africa and the Mojave in California, the Atacama is actually a very cool place with an average daily temperature between 0 ° C and 25 ° C.
Although it seems difficult that there is life in the Atacama, the holes are isolated and small areas of plants that provide a life of some insects and animals. Some plants are very well adapted to this arid environment, the development of long roots that reach to the water below the ground.Since the Andes mountain ranges active volcano, magma pressure of underground water in certain places causing geysers.

The Atacama Desert is probably the oldest desert on earth and has experienced extreme hyperaridity for at least 3 million years and probably 15 million years.The climate of the Atacama Desert is largely controlled by its zonal location between 15° and 30°S in the sub-tropical high-pressure belt where descending stable air produced by the Hadley circulation significantly reduces convection and hence precipitation.

Special attractions are the huge salt lake “Salar de Atacama”, which is almost dried out, and the bizarre landscape formations like the “Valley of the Moon” or the hot springs “Tatio Geysers”.

Monday, March 21, 2011

Yellowstone supervolcano

Yellowstone is the largest supervolcano on Earth!Most volcanoes that produce super-eruptions are very long-lived (active over millions of years), produce very large explosive eruptions, and remain dormant for long periods (from thousands to hundreds of thousands of years) between major eruptions.The Yellowstone supervolcano last erupted approximately 630,000 years ago. Scientists believe that it’s now overdue a repeat performance….
Beneath the beauty of America’s first national park is a killer volcano that is 1,000 times more powerful than Mt. Saint Helens and hundreds of times more powerful than all the volcanos in Iceland …combined! Yellowstone was set aside to protect and preserve its treasure of geothermal features—over 10,000 of them! Geysers are the most famous of these features— half of the world’s 700 geysers are located in Yellowstone.Three giant calderas in the western US, all formed in the last 1 million years include the Yellowstone hot-spot and two rift related supervolcanoes, Long valley caldera in eastern California and Valles caldera along the edge of the Rio Grande river in New Mexico.Each covered large areas of the US with volcanic ash when they last erupted.Although giant calderas (“supervolcanoes”) may slumber for tens of thousands of years between eruptions, their abundant earthquakes and crustal deformation reveal the potential for future upheaval.The super volcano at Yellowstone, and its kin around the world are a credible threat to man.“Yellowstone supervolcano could erupt again and when it does the whole world will be transformed.Yellowstone is located in the Rocky Mountain chain, but its geological story is different.At Yellowstone, the large thermal and CO2 fluxes require massive input of basaltic magma, which continues to invade the lower to mid-crust, sustains the overlying high-silica magma reservoir, and may result in volcanic hazard for millennia to come.

Sunday, March 20, 2011

Super volcano eruptions

In the past, several super vulcano eruptions sufficiently large to cause a global disaster have occurred, on average, every 100,000 years.Most volcanoes that produce super-eruptions are very long-lived (active over millions of years), produce very large explosive eruptions, and remain dormant for long periods (from thousands to hundreds of thousands of years) between major eruptions.The appearance of the volcano itself after eruption is also distinctive: it doesn’t conform to the common image of a volcano as a lofty, symmetrical, conical structure.The power of a volcano is measured by how much magma and ash it produces. A supervolcano is the biggest, most destructive volcano.Supereruptions require a very large volume of magma with strong explosive potential. Explosive potential results from a high content of volatile constituents (mostly H2O) that can form gas bubbles, combined with high viscosity to inhibit escape of the bubbles from the magma; it is the bursting of these trapped bubbles that drives an explosion. Supereruptions are “the ultimate geologic hazard,” in terms of the immediate and devastating impact of eruption products on our social infrastructure, and with regard to the longer-term climatic effects that will arise from loading the stratosphere with sulfur-rich gases.A supervolcano eruption packs the devastating force of a small asteroid colliding with the earth and occurs 10 times more often—making such an explosion one of the most dramatic natural catastrophes humanity should expect to undergo.Yellowstone is the largest super volcano on Earth!Beneath the beauty of America’s first national park is a killer volcano that is 1,000 times more powerful than Mt. Saint Helens and hundreds of times more powerful than all the volcanos in Iceland …combined!

How volcanoes erupt

Many of us are interested in how volcanoes erupt.
Many large volcanoes on Earth are capable of explosive eruptions much bigger than any experienced by humanity over historic time.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.This is how volcanoes erupt.
The molten rock that comes out of a volcano has been brought to the surface by a combination of things. The main one is the force of gravity: the molten rock is not as dense as the rocks around it so it tries to go upwards, just as the heated wax in a lava lamp will rise.
The gases dissolved in it are also one thing that helps it erupt (like carbon dioxide and sulphur dioxide), which come out as bubbles as the pressure reduces when it nears the surface and can force it out explosively, a bit like when you shake up a Coke bottle and take the top off: the gas forces out the Coke in a fountain.
Most gases from a volcano quickly blow away. However, heavy gases such as carbon dioxide and hydrogen sulfide can collect in low-lying areas.Although gases usually blow away rapidly, it is possible that people who are close to the volcano or who are in the low-lying areas downwind may be exposed to levels that may affect health.At depth in the Earth nearly all magmas contain gas dissolved in the liquid, but the gas forms a separate vapor phase when pressure is decreased as magma rises toward the surface of the Earth.In 1984, CO2 gas escaping from the bottom of Lake Monoun, a crater lake in the African country of Cameroon, killed 37 people.In 1986 an even larger CO2 gas emission from Lake Nyos in Cameroon killed more than 1700 people and 3000 cattle.Clouds of gas and tephra that rise above a volcano produce an eruption column that can rise up to 45 km into the atmosphere. Eventually the tephra in the eruption column will be picked up by the wind, carried for some distance, and then fall back to the surface as a tephra fall or ash fall.

Saturday, March 19, 2011

Earthquake location

There are several methods used to locate earthquakes, triangulation is one that uses distance information from 3 or more stations to uniquely locate an earthquake.For an earthquake at the surface there are three unknowns: latitude, longitude, origin time.Triangulation is a method that uses distance information determined from 3 seismic stations to uniquely locate the earthquake.
An earthquake location specifies the place and time of occurrence of energy release from a seismic event.The location may refer to the earthquake's epicentre, hypocentre, or centroid, or to another observed or calculated property of the earthquake that can be spatially and temporally localized.An earthquake epicenter can be located from records made of earthquake waves on devices called seismographs.
A location is called absolute if it is determined or specified within a fixed, geographic coordinate system and a fixed time base, a location is called relative if it is determined or specified with respect to another spatio-temporal object which may have unknown or uncertain absolute location.We can locate earthquakes using a simple fact: an earthquake creates different seismic waves (P waves, S waves, etc.) The different waves each travel at different speeds and therefore arrive at a seismic station at different times.
For rapid hazard assessment and emergency response, an earthquake location provides information such as the locality of potential damage or the source region of a possible tsunami, and a location is required to calculate most measures of the size of an earthquake, such as magnitude or moment.
Since earthquakes occur deep in the Earth, their source locations must be inferred indirectly from distant observations, and earthquake location is thus a remote-sensing problem.

Wednesday, March 16, 2011

Earthquakes causes and effects

Here, i have tried to explain the nature, distribution, causes and effects of this terrifying natural event.A large number of earthquakes are felt all over the globe every year.Most human lives in earthquakes are lost due to collapse of houses. Styles of making houses depend on local climate, construction material available and on local traditions. The small ones are unnoticed while the large ones are felt over thousands of kilometers.When the earthquake struck, the longer, more flexible columns at the front of the building passed the earthquake forces on to the short, stiffer columns in the back instead of distributing the forces equally among all of the columns.Many properly executed buildings are not safe against earthquakes, simply because their foundations were made without considering the earthquake hazard.When an earthquake occurs in a populated area, it may cause deaths and injuries and extensive property damage.
Different types of seismic waves  produce the violent ground shaking, or motion, associated with earthquakes.These wave vibrations produce several different effects on the natural environment that also can cause tremendous damage to the built environment (buildings, transportation lines and structures, communications lines, and utilities).Ground shaking from earthquakes can collapse buildings and bridges; disrupt gas, electric, and telephone service; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive, seismic sea waves called tsunamis.
Tsunami (“Soo na me”) is Japanese for tidal wave. A tsunami is caused by an earthquake, landslide, or volcanic eruption on the sea floor. Tsunamis are often no taller than normal wind waves, but they are much more dangerous.Tsunamis run quickly over the land as a wall of water.

Friday, March 11, 2011

Moon closest to earth

Moon closest to Earth since 1992nd.
19th March this year, the moon will be closest to Earth at a distance of only 356 577 km, What is the closest distance since 1992. The event, which is known as the lunar perigee will provide a unique opportunity for fantastic photos, but some scientists warn that it could disrupt the Earth's climate and cause earthquakes and volcanic activity.
Previous such events were associated with extreme weather, so in 2005. the tsunami killed hundreds of thousands of people, and 1974th the cyclone has devastated Australia.The Earth is thus closer to the moon 1955th, 1974., 1992. and 2005. year, all of which are marked by extreme storms. Before six years before the tsunami in Indonesia has killed hundreds of thousands of people, and 1974th The Cyclone Tracy devastated Australia.
Speculation of some scientists that this moon approaching could cause earthquakes and volcanic activity it may be true.For all the natural disasters are associated with some events in the night sky - a comet, planet, sun or moon.
While others do not agree with it and say:There will be no earthquakes or volcanic eruptions that would not be possible and otherwise.The Earth will experience only minor changes to low tide and larger changes in the tide, but it is nothing about which to be excited.The gravity of the moon is tugging on the Earth and causing a slight sort of distortion as the moon orbits the Earth and that leads to tides eventually.

Monday, March 7, 2011

Mariana trench depth

The Mariana trench has a maximum depth of 10,971 m (35,994 feet) below sea level, called Challenger Deep. It is located east of the Mariana Islands at 11°21`N, 142°12`E, near Guam. Mariana Trench was discovered in 1872. First they reached the Swiss Jacques Piccard and Don Walsh from America in 1960. Mariana Trench was formed at the point where it meets the bottom of the Pacific and Philippine tectonic plates. Its deepest parts are formed before 6-9 000 000 years. Mariana Trench is 23% deeper than it is Mount Everest high.


Mariana Trench is not only the deepest point of the Pacific Ocean, but the deepest point in the world. Data on its depth constantly vary, but the last say as its depth 12 111 feet below sea level.
 At the bottom of the Mariana trench pressure is more than a thousand times greater than standard atmospheric pressure at sea level. However, that living beings can adapt to such pressures, Japanese scientists have proven that at 11 km depth reveal the microscopic organisms.
The origin of this huge underwater Valley is the result of movement of lithosphere plate.
Microscopic single-celled organisms, including many unknown, were discovered in the deepest parts of the Pacific Ocean at 10 896 feet deep, according to Japanese scientists. These organisms are found in the piece sinks of sediment from the Challenger southwest of the island of Guam, Mariana Trench in the Pacific. These organisms probably can survive by absorbing particulate organic matter dropped from the surface or substance that is dissolved in salt water.
Deep trenches, such as the Japan Trench, the Izu-Ogasawara Trench, the Mariana Trench, the Yap Trench, the Palau Trench, the Philippine Trench, and the Nansei- Shoto (Ryukyu) Trench are present in the western North Pacific Ocean.


Saturday, March 5, 2011

Mesosphere facts

Here ar some interesting facts about mesosphere.The mesosphere cools with increasing height until it reaches the mesopause or minima with summer temperature at about −130 °C or lower, then it starts to warm again with height in the lower thermosphere. The mesosphere extends from between 31 and 50 miles (50 to 80 kilometers) above the earth's surface. The mesosphere is characterized by temperatures that quickly decrease as height increases with temperatures as low as -93°C at the top of the layer. Only rockets and meteors travel through this layer.And this is where meteors usually burn up when they enter Earth’s atmosphere.The mesosphere is the coldest layer of the atmosphere, where the thin air is often turbulent and strong gusty winds blow—it even contains ice aerosol clouds in summer.The boundary between the stratosphere and the mesosphere is known as the stratopause.The percentage of Nitrogen and Oxygen is about the same in the mesosphere as it is at sea level but the atmospheric pressure is much lower. The lapse rate in the mesosphere is approximately 2°C/1000 m.The mesopause marks the boundary between the mesosphere and the thermosphere.Due to reactions taking place in the thermosphere and upper mesosphere, mesospheric air is enhanced in reactive nitrogen compounds, which can effect ozone. Furthermore, mesospheric
air is enhanced in CO  and is expected to show enhanced levels of molecular hydrogen and depleted values of water vapour, which may influence the chemistry of OH radicals.Long-period oscillations in the period range between 2-30 days, interpreted as planetary wave (PW) signatures, have been analysed using daily upper mesosphere/lower thermosphere wind measurements near 90 km over Collm (52°N, 15°E) in the time interval 1980-2005. Strong interannual and interdecadal variability of PW are found.

Lahars

Lahars are rapidly flowing mixtures of rock debris and water that originate on the slopes of  a volcano.Explosive eruptions can deposit huge amounts ash and other volcanic debris on a volcano’s slopes. Lahars form when water from intense rainfall, melting snow and ice, or the sudden failure of a natural dam, mixes with this loose volcanic material, creating mudflows that can be particularly dangerous and destructive.Volcanic eruptions may directly trigger one or more lahars by quickly melting snow and ice on a volcano or ejecting water from a crater lake.Although lahars contain at least 40% (by weight) volcanic ash and rock fragments—making them dense and viscous like wet concrete—they actually flow faster than clear-water streams.
As it rushes downstream, its size, speed, and the amount of water and rock debris it carries are constantly changing.Lahars can fall under three categories of classification, syn-eruptive, post-eruptive or
non-eruptive.Primary (syneruptive) lahars can occur when an eruptions
melts ice or a crater lake is breached.Secondary lahars can result
from debris avalanches (landslides) or from erosion of fresh, unconsolidated pyroclastic material.

Lahars Deposits
Because of bed friction, bottom layers move more slowly
-Consequently, larger particles work toward the front and margins
- Lower concentration flows can be normally graded as coarse material settles first
- Inverse grading is a consequence of “kinetic sieving”

Lahars have been the cause of major damage and loss of life throughout history. They have buried entire towns, and destroyed cities beyond repair.Their extreme danger makes them an important topic of research throughout the geosciences in the hopes of mitigating future disaster.
Lahars have the strength to rip huge boulders, trees, and man-made
structures from the ground, carrying them for great distances.

Thursday, March 3, 2011

Unsafe building

Buildings with foundations resting on unconsolidated landfill and other unstable soils are at increased risk of damage.When an earthquake occurs in a populated area, it may cause deaths and injuries and extensive property damage.Entry into damaged unsafe buildings as soon as possible is often necessary for a variety of emergency reasons, including search and rescue, building stabilization and repair, and salvage and retrieval of possessions.We must all work together in our communities to apply our knowledge to enact and enforce up-to-date building codes, retrofit older unsafe buildings, and avoid building in hazardous areas, such as those prone to landslides.
For buildings considered stable, wait times depend on the main shock magnitude and the duration of occupancy, as both of these factors affect the probability of a large aftershock occurring during the period of occupancy.Because the aftershock hazard diminishes with time, it is possible to determine in general when the risk of entering
an UNSAFE building, for a given period of time, reaches an acceptable level.Cold-formed steel has become a popular building material for commercial and industrial buildings.Slices of cold-formed steel, which is normally used for braiding low and medium high-rise buildings, are made by bending sheet metal approximately one millimeter thick, without heating, the structural forms. These components are usually easier and cheaper than traditional construction systems and have other advantages. For example, pieces of cold-formed steel are more homogeneous than the wooden components and does not possess the sensitivity of the termite and wood rot.Structural engineers who designed the building from cold-formed steel should provide more data on how the material will behave during an earthquake.
We must also look for and eliminate hazards at home, where our children
spend their days, and where we work. And we must learn and practice what to do if an earthquake occurs.

Tuesday, March 1, 2011

Ground shaking

Ground shaking from earthquakes can collapse buildings and bridges, disrupt gas, electric, and telephone service, and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive, seismic sea waves called tsunamis.
An earthquake is a sudden movement of the Earth caused by the abrupt release of energy that has accumulated over a long time.
Objective is to estimate the ground shaking from a specified earthquake, sometimes called a scenario earthquake.In seismic design, characteristics of the maximum ground shaking are desired.
For hundreds of millions of years, the forces of plate tectonics have shaped the earth as the huge plates that form the surface move slowly over, under, past, and away from each other.
The ground shakes or vibrates as the seismic waves cause small temporary displacements of the ground.At the surface, the ground moves vertically up and down and horizontally back and forth.The strength and frequency of seismic waves and the length of time strong shaking lasts all affect the amount of damage caused by ground shaking.
When an earthquake occurs in a populated area, it may cause deaths and injuries and extensive property damage. Buildings with foundations resting on unconsolidated landfill and other unstable soils are at increased risk of damage. The effects of earthquake ground shaking depend on the specific response characteristics of the type of structural system used.
Ground shaking may also trigger soil liquefaction, landslides, and other types of ground failure, which can also cause damage.
Initial effects of an earthquake are violent ground motions which can produce cracks or fractures in the ground and liquefaction, where loose sandy soils with a high moisture content separate and give the surface a consistency much like that of quicksand.