Category Earth Science

This machine is used to measure the force of the vibrations caused by an earthquake. It records how powerful these vibrations are on a numbered scale.

 They are held in a very solid position, either on the bedrock or on a concrete base. The seismometer itself consists of a frame and a mass that can move relative to it. When the ground shakes, the frame vibrates also, but the mass tends not to move, due to inertia. The difference in movement between the frame and the mass is amplified and recorded electronically.

A network of seismometers is used to calculate the magnitude and source of an earthquake in three dimensions

Seismographs are used to determine:

• Magnitude: the size of the earthquake
• Depth: how deep the earthquake was
• Location: where the earthquake occurred

 

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The plates in Earth’s crust constantly side past each other, but can get stuck. Pressures then builds up until the plates finally move, sending out shock waves. The focus of an earthquake is the point inside the ground where pressure builds up. The epicenter is the point on the surface above the focus.

The point at which this slippage occurs is called the FOCUS, whilst the point on the ground surface above the earthquake FOCUS is called the EPICENTRE. Seismic shock waves will emanate radially outwards from these points and their energy will reduce with distance. This is typical of destructive margins (which account for 90% of the World’s earthquakes) where the Oceanic plate grinds under a Continental plate (as on the East coast of Japan -see Kobe case study). They also occur at conservative margins, such as the San Andreas Fault line, where the North American plate and Pacific plate are grinding past one another.

 

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An earthquake can cause large cracks to open up in the Earth’s surface. Many are small, no more than a few metres deep or wide, but others are massive, and whole buildings can fall into them.

When an earthquake strikes, it will create fissures into the depths of the earth in random locations, usually with a lot of people. In reality, the ground often just shakes, shifts and quakes — the physical damage is usually to structures on the ground, not the ground itself. If fissures do open up, it is usually due to a landslide triggered by the quake, which means they’re restricted to hillsides, mountains, and cliffs. If you see roads with cracks and fissures and dislodged pieces, it is because the wet, sandy ground underneath has liquefied, causing the road to sink unevenly and crack. And yes, that can happen to buildings too.

 

Picture Credit : Google

When the rocky tectonic plates that form Earth’s crust move suddenly, large waves of energy spread out, causing the ground to shake. This is an earthquake. Some earthquakes are fairly gentle and may even go unnoticed, but others can bring terrible destruction.

Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens. The largest, main earthquake is called the mainshock. Mainshocks always have aftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock!

 

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The magma chamber: This is the area with massive collection of magma below the earth’s crust from which magma flows out.

Crater: After an eruption, the tip or top of the volcano tends to get blown off, leaving a small depression at the top of it.

Main vent: This is the main exit point (opening or outlet) in a weak zone where molten magma is released to the surface.

Secondary vents: These are other smaller vents or opening through which ash and gases and lava escape.

Ashes, clouds and cinders: As the eruption continues, ashes and gases are discharged into the air, which is carried further by wind action.

Layers of ash and lava: The walls of a volcano are usually made up of solidified layers of lava and dust.

 

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Volcanoes form when magma a mixture of hot gas, ash, and melted rock-erupts from a crack in the Earth’s surface. The melted rock, called lava, flows out and hardens. As layers of lava build up, the volcano gets bigger. A volcano can be active, dormant, or extinct. Volcanoes can and have existed on other worlds as well: although volcanoes on the moon and Mars have long been dormant, volcanoes are still very active on Jupiter’s moon Io. Researchers are currently striving to find ways to predict when volcanic eruptions might happen on Earth by analyzing clues such as crystals and gases linked with volcanoes.

Stratovolcano

Stratovolcanoes are tall and cone-shaped, with steep sides. They are made up of lots of layers of lava and ash that have cooled and hardened. Their eruptions can be very powerful and dangerous.

Stratovolcanoes are also called composite volcanoes because they are built of layers of alternating lava flow, ash and blocks of unmelted stone, according to the U.S. Geological Survey. They are larger than cinder cones, rising up to 8,000 feet (2,438 meters). Stratovolcanoes result from a conduit system of vents leading from a magma reservoir beneath the surface. When dormant, they typically have steep concave sides that sweep together at the top around a relatively small crater.

Shield   

Shield volcanoes have gently sloping side and are formed from thin, runny lava. Their eruptions are less explosive and much less dangerous than other volcanoes. These gentle eruptions can continue for years. Eruptions of these volcanoes are not generally explosive, but are more like liquid overflowing around the edges of a container. The world’s largest volcano, Mauna Loa in Hawaii, is a shield volcano, according to the U.S. Geological Survey. Mauna Loa is about 55,770 feet (17,000 meters) from its base beneath the ocean to the summit, which is 13,681 feet (4,170 meters) above sea level. It is also one of the Earth’s most active volcanoes and is carefully monitored. The most recent eruption was in 1984.

Cinder Cone

Cinder cone volcanoes are the smallest and most common type of volcano. They are cone-shaped with steep sides. Their eruptions are usually not too violent. They may occur as single volcanoes or as secondary volcanoes known as “parasitic cones” on the sides of stratovolcanoes or shield volcanoes. Airborne fragments of lava, called tephra, are ejected from a single vent. The lava cools rapidly and fall as cinders that build up around the vent, forming a crater at the summit, according to the U.S. Geological Survey.

Caldera

Calderas are large, circular hollows, almost like a bowl. They form when a massive eruption forces most of the magma out of the chamber under the volcano, causing it to collapse. Craters are usually more circular than calderas. (Calderas may have parts of their sides missing because land collapses unevenly.) Craters are also usually much smaller than calderas, only extending to a maximum of one kilometer (less than a mile) in diameter. 

 

Picture Credit : Google