Test: Our Changing Earth - 2

• The location inside the Earth where an earthquake begins is called the focus (or hypocenter) of the earthquake.
• The point at the Earth's surface directly above the focus is called the epicenter of the earthquake.
• At the epicenter, the strongest shaking occurs during an earthquake.

• The Richter scale measures the magnitude of an earthquake. It is measured using a machine called a seismometer which produces a seismograph.
• A Richter scale is normally numbered 1-10, though there is no upper limit.
• Generally, seismometer consists of a mass attached to a fixed base. During an earthquake, the base moves and the mass does not.

• Bhuj is a city in the state of Gujarat, western India.
• It’s known for its centuries-old buildings, many of which were damaged in a 2001 earthquake. Close to Harmirsar Lake, the 18th-century Aina Mahal palace is elaborately decorated with chandeliers, mirrors and semi-precious stones.
• Nearby, the Italian Gothic–style Prag Mahal palace has a bell tower that overlooks the city, and a courtyard containing a Hindu temple.

• The 2001 Gujarat earthquake, also known as the Bhuj earthquake, occurred on 26 January, India's 52nd Republic Day, at 08:46 AM IST and lasted for over 2 minutes.
• The epicentre was about 9 km south-southwest of the village of Chobari in Bhachau Taluka of Kutch District of Gujarat, India.

Being near the windows may cause an injury as the tremors may lead to broken glass.

The correct option is Option A.

Seismic waves are waves of energy that travel through the Earth's layers, and are a result of earthquakes, volcanic eruptions, magma movement, large landslides and large man-made explosions that give out low-frequency acoustic energy.

The epicentre or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates.

The hypocenter is the point within the earth where an earthquake rupture starts. The epicenter is the point directly above it at the surface of the Earth. Also commonly termed the focus.

• A major earthquake registers between 7 and 7.9 on the Richter scale. There are about 20 a year worldwide and they cause very serious damage.
• Intensity 7 is very strong. Damage is negligible in buildings of good design and construction, slight to moderate in well-built ordinary structures, considerable damage in poorly built or badly designed structures.

Erosion is wearing away of landscape by agents like water, wind, ice etc

Angel Falls in Venezuela is the world's tallest waterfall, with a total height of 3212 feet (979 meters). This total height includes a single uninterrupted drop of 2648 feet (807 meters), plus 564 feet (172 meters) of steep cascades and smaller drops downstream from the main falls.

• Fine particles of pulverized rock blown from an explosion vent. Measuring less than 1/10 inch in diameter, ash may be either solid or molten when first erupted.
• By far, the most common variety is vitric ash (glassy particles formed by gas bubbles bursting through liquid magma).

The running water in the river erodes the landscape. When the river tumbles at steep angle over very hard rocks or down a steep valley side it forms a waterfall.

The meander loop cuts off from the river and forms a cut-off lake know as mender lake. As the river enters the plain it twists and turns forming large bends known as meanders.

• The steep rocky coast rising almost vertically above sea water is called seacliff.
• The sea waves deposit sediments along the shores forming beaches.
• Glaciers are “rivers” of ice which too erode the landscape by bulldozing soil and stones to expose the solid rock below. Glaciers carve out deep hollows.

Wind is an active agent of erosion and deposition. In deserts we can see the rocks in the shape of mushroom due to the erosion of the lower part of the rock that is why mushroom rocks have wider top and narrower base.

• The sea caves occur on the cliffed coast of the study area where the waves break directly on the rock cliff.
• Mechanical erosion along with chemical solution process is responsible for the formation of the caves.
• Deep inlets are formed through the zones of weakness under the force of waves and are eroded out.

• In deserts you can see rocks in the shape of a mushroom, commonly called mushroom rocks.
• Winds erode the lower section of the rock more than the upper part. Therefore, such rocks have narrower base and wider top.

When the wind blows, it lifts and transports sand from one place to another. When it stops blowing the sand falls and gets deposited in low hill – like structures. These are called sand dunes.

• Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometer size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate.
• Extensive loess deposits are found in northern China, the Great Plains of North America, central Europe, and parts of Russia and Kazakhstan.
• The thickest loess deposits are near the Missouri River in the U.S. state of Iowa and along the Yellow River in China.
• Loess accumulates, or builds up, at the edges of deserts.

• Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometer size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate.
• Coastal landforms created by erosion include headlands, bays and cliffs. Landforms created by deposition include spits, salt marshes and beaches.

Conditions for delta formation by a river:

• The river must have gentle gradient in its lower course.
• The river must carry large amount of sediments along it.
• The coastal plains or area where mouth of river lies should be wide.

=>Though Narmada originates far from Western Ghats and empties into the Arabian Sea, the river flows through a rift valley at a steep gradient which increases its speed. Also, the west coastal plains are less wider than that required for delta formation by Narmada.