INTERIOR OF THE EARTH 

The earth has a huge size and changing nature of its interior composition. Due to this, it is not possible to know about the interior of the earth by direct observations. The earth’s radius is 6,370 km. Humans can't reach the centre of the earth. Through mining and drilling operations we have been able to observe the earth’s interior directly for a depth of a few kilometres. The rapid increase in temperature below the earth’s surface is mainly responsible for setting a limit to direct observations inside the earth.

Rocks from the mining areas Scientists overworld working on different projects to explore the conditions in the crustal portions. Deep Ocean Drilling Project and Integrated Ocean Drilling Project are two important projects. The deepest drill at Kola, in the Arctic Ocean, has so far reached a depth of 12 km.

Volcanic eruptions

Earthquakes are shaking the earth. It is caused by to release of energy, which generates waves to travel in all directions. The point where energy is released is called the focus or hypocentre of the earthquake. The point on the surface of the earth is called the epicentre.it is the point directly above the focus.

Seismographs are instruments used to record the motion of the ground during an earthquake. Earthquake waves are basically of two types- body waves and surface waves. Body wave moves through the interior of the earth, as opposed to surface waves that travel near the earth's surface. There are two types of body waves-P and S waves.

• P- Waves or primary waves move faster and reach the surface. These are similar to sound waves and parallel to the direction of the wave. P-waves travel through gases, liquid and solid materials. The body waves interact with the surface rocks and generate a new set of waves called surface waves.
• These are secondary waves. S-waves arrive at the surface with some time lag and travel only through solid material. S- Waves are perpendicular to the wave direction, hence these are more destructive, and they cause the displacement of rocks leading to the collapse of the structures.
• The emergence of the shadow zone: The shadow zone is the zone of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves.  It results from P waves being refracted by the liquid core and S waves being stopped completely by the liquid core.

Types of earthquakes

The most common ones are tectonic earthquakes. These are generated due to the sliding of rocks along a fault plane.

1. A volcanic earthquake is caused by the movement of magma beneath the surface of the Earth. 
2. Collapse earthquakes are small earthquakes in underground caverns and mines that are caused by seismic waves produced from the explosion of rock on the surface.
3. Explosion earthquakes are produced by the detonation of chemicals or nuclear devices.

• The earthquake events are scaled according to the Magnitude or intensity of the shock. The magnitude scale is called the Richter scale and is expressed in absolute numbers 0-10.
• The intensity scale is named after Mercalli, an Italian seismologist. It takes into account the visible damage. The range of the intensity scale is from 1 to 12.
• The immediate hazardous effects of the earthquake area include ground shaking, differential ground settlements, land and mudslides, soil liquefaction, ground lurching, avalanches, ground displacement, floods from dam and levee failures, fires, structural collapse, falling objects and tsunamis.
• The effect of the tsunami would occur only if the epic centre of the tremor is below the oceanic waters and the magnitude is high. Tsunami waves are generated by tremors and not an earthquakes themselves. The quakes of the high magnitude are rare and tiny types occur every minute.

2. Structure of the Earth

3. Volcanoes and Volcanic Landforms

A volcano is defined as an opening in the Earth's crust through which lava, ash, and gases are erupting. 

Shield volcanoes are the largest volcanoes on the earth, for example, the Hawaiian volcanoes. Active volcanoes are mostly made up of basalt [a type of lava that is very fluid when it erupts].

1. Caldera: These are the most explosives in the earth's volcanoes. They tend to collapse on themselves rather than build any tall structure. The collapsed depressions are called calderas.
2. Flood basalt provinces: These volcanoes outpour highly fluid lava that spreads long distances. Some parts of the world are covered by thousands of km of thick basalt lava flows. The lava thickness is 50-100 meters, and the Deccan traps from India, presently cover the Maharashtra plateau.

Mid–Ocean Range Volcanoes: These volcanoes occur in oceanic areas and their ridges are more than 70,000 km long that stretch through all the ocean basins.

Volcanic Landforms

Lacoliths: These are larger dome-shaped intrusive bodies with a level base connected by a pipe-like conduit from below and located in the deeper depths. The Karnataka plateau is spotted with domed hills of granite rocks.

Lalith, phytolith and sills: An igneous intrusion is associated with a structural basin, with contacts that are parallel to the bedding of the enclosing rocks. A phytolith is a pluton of igneous rock parallel to the bedding plane or foliation of folded country rock.  The near horizontal bodies of the intrusive igneous rocks are called sill or sheets. The thicker one is called sheets and the thinner one is called sills.

Dykes: When lava makes its way through cracks the fissures develop in the land and solidify almost perpendicular to the ground. It gets cooled in the same position to develop a wall-like structure called dykes. These are mostly found in intrusive forms in the western Maharashtra area. These are considered the feeders for the eruptions that led to the development of Deccan traps.