Our changing earth - class-IX

Young folded mountains are located at tectonic plate boundaries where crustal movement is most active, making them the most prone to seismic activity and earthquakes.

An isoseismic line is a line on a map connecting points where an earthquake has the same intensity. Isobars connect points of equal pressure, and isotherms connect points of equal temperature.

An earthquake is defined as the shaking or vibration of the Earth's surface caused by the release of energy from the crust, typically due to tectonic plate movement.

An earthquake is the sudden shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can be violent enough to toss people around and destroy whole cities. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.

Rotation is the movement of the earth on its axis. The earth takes about 24 hours to complete one rotation on its axis. The period of rotation is known as the earth day. This is the daily motion of the earth.

Glacial deposition is the settling of sediments left behind by a moving glacier. As glaciers move over the land, they pick up sediments and rocks. The mixture of unsorted sediment deposits carried by the glacier is called glacial till. Piles of till deposited along the edges of past glaciers are called moraines.

Drumlin, oval or elongated hill believed to have been formed by the streamlined movement of glacial ice sheets across rock debris, or till. The name is derived from the Gaelic word druim (“rounded hill,” or “mound”) and first appeared in 1833.

Larger pieces of rock that are encrusted in till or deposited on the surface are called "glacial eratics". They range in size from pebbles to boulders, but as they are often moved great distances, they may be drastically different from the material upon which they are found.

Fluvioglacial landforms are landforms molded by glacial meltwater. This discharge of glacial streams, both over the surface and beneath the ice sheet, is higher in the warmer summer months. As subglacial water often flows under pressure, it has a high velocity and is very turbulent.

The Earth is a non-luminous body but the sun is luminous. As the earth is rotating around its axis, half of its portion is facing the sun and the other half is entirely dark due to the absence of sun. In other words, half of the globe have day and on the other half, it is a night. As the earth is rotating around the sun its every part is exposed to Sun within every 24 hours this rotation causes days and nights.

Barkan is a crescent-shaped sand dune produced by the action of wind predominately from one direction. One of the commonest types of dunes, it occurs in sandy deserts all over the world.

Earth takes about 365 1/4 days to revolve around the sun. As we take 365 days for a year, the difference of 1/4 of a day requires adjustment. This is why we add one day to February every four years.

The axis is an imaginary line passing through the centre of the Earth. Its two ends on the surface are called north and south poles.

1;The earth rotates around its vertical axis. The axis is an imaginary line passing through the centre of the earth. Its two ends on the surface are called North and South poles The Earth completes one rotation in 24 hours. 

Tilted axis and vertical axis are present respectively in Earth and Pluto.

Wind erosion has the greatest impact on areas with dry soil because it is easier for wind to pick up and transport dry, light soil. Characteristically, deserts have dry soil, or sand, that is easy to transport. Also, deserts often have fewer physical barriers, such as hills, trees, or other structures, that can slow the wind movement.

Erosion is the geological process in which earthen materials are worn away and transported by natural forces such as wind, water, or ice.

Earthquake refers to a sudden violent shaking and vibration of the earth's surface resulting from underground movement along a fault plane or from volcanic activity. Earthquakes can cause serious destruction to property, injury to people and even death. It happens when there is sudden movement or breaking of the tectonic plates.

Moraines are accumulations of dirt and rocks that have been pushed along by a glacier as it moves, often forming ridges at the edges.

Glaciers and ice caps hold approximately 70% of the world's total freshwater supply, although this is a significant portion of the total water on Earth.

The moving ice mass downslope under the impact of gravity is called a glacier. About 10 percent of the earth's surface is now covered by the glacier. Glacier is formed due to the accumulation of ice above snow-line under extreme cold climate.

Cirque is a bowl-shaped, amphitheater-like depression eroded into the head or the side of a glacier valley. Typically, a cirque has a lip at its lower end. A cirque may also be a similarly shaped landform arising from fluvial erosion.

Ice is the poorest sorter of sediment. Glaciers can transport almost any size sediment easily, and when ice flow slows down or stops, the sediment is not deposited, due to the density of the ice. As a result, sediments deposited directly by ice when it melts are usually very poorly sorted. Significant sorting only occurs in glacial sediments that are subsequently transported by melt water from the glacier. Wind, on the other hand, is the best sorter of sediment, because it can usually only transport sediment that ranges in size from sand to clay. Occasional variation in wind speed during transport serves to further sort out these sediment sizes.

When glaciers melt or recede they deposit the rock materials brought by them in heaps of various shapes and size. These are known as moraines. Moraines are depositional feature and consist of rock materials of heterogeneous shape and size.