Important Question And Answer: Civil - Engineering Geology - Physical Geology

1) Write notes on Lithosphere.

Litho is a Greek word, which means stone. Accordingly the lithosphere is the part of the earth, which is solid crust. The thickness of lithosphere is approximately 50 km. The crust thickness is not the some at all places. It is thicker in the continent and thinner on the ocean floors. Lithosphere is a source of various minerals. It contains variety of landforms such as mountains.plateous valleys, plains.

2) What is meant by NIFE?

The central part of the earth is called Core or barysphere. It has thickness of 2900km.This layer is made of very hard mineral like Nickel (Ni) and iron (Fe) and so it is called NIFE (Ni + Fe). Here there is intense heat and pressure and this region is elastic and viscous in nature.

3) Distinguish between SIAL and SIMA.

The upper most layers is called the crust of the earth. It has a thickness of 50 km and thus the crust is made of two layers. Silica (si) and Aluminium (Al) are the elements found in the first layer. Therefore this layer is called SIAL (Si + Al). This layer is also called 'Granitic layer.'

Below the SIAL ties a layer called SIMA which composes of silica (Si) and Magnesium (Mg). This layer is also called Basaltic layer.

4) What are plates?

The surface of the earth is the crust of the earth. It is made of interlocking pieces called plates. The continents and oceans rest in these places and are separated by wide cracks. The plates move constantly.

5) What is meant by atmosphere?

The outer gaseous part of the earth starting from the surface and extending as far as 700 km and even beyond is termed atmosphere.It makes only about one-million part of the total mass of the earth.

6) Define sea floor spreading.

Divergent boundaries occur at Oceanic ridges. In the process of plate separation, the magma rises up from the asthenosphere and fills the gap their created. In this way new crust is created along the trailing edges of the diverging plates. This phenomenon is called sea floor spreading.

7) What are the subdivisions in geology?

The subdivisions are:

a)     Physical geology

b)        Geomorphology

c)     Mineralogy

d)    Petrology

e)       Historical geology

f)       Economic geology

g)     Geohydrology

h)     Engineering geology

i)       Metrology

8.What is meant by engineering geology?

Engineering geology may be defined as that of applied sciences which deals with the application of geology for a safe, stable land economical design and construction of a civil engineering project.

9) Define seismology.

Seismology is a branch of geophysics that deals with the study of elastic waves within the body of the earth during an earthquake.ie.The study of earthquake is called seismology.

10) Give the two types of discontinuity.

There are two important discontinuities:

Mohorovocic or Moh discontinuity Gutenberg or Oldharm discontinuity

11)           Define denudation.

It is general term used when the surface of the earth is worn away by chemical as well as mechanical actions of physical agents and the lower layers are exposed. This happens when the rocks were exposed for a sufficient length of time to the attacks of physical agents.

12) What is mean by continental crust?

The continental crust consists of two layers separated by a well-defined discontinuity known as conard discontinuity. The layers have been defined on the basis of seismic waves velocities and densities.

In the upper layer the velocity of seismic waves corresponds to the velocity found by experimental to be characteristic of granite. Hence they are called as Granitic or sialic layer.

13) What is mean by physical weathering?

It is a physical breakdown of rock masses under the attack of certain atmospheric agents. A single rock block is broken gradually into smaller irregular fragments and then into particles of still smaller dimensions. Temperature variations are irresponsible to a great extent of physical weathering.

15) Define deflation.

Deflation is the process of simply removing the loose sand and dust sized particles from an area, by fast moving winds. Wind deflation can successfully operate in comparatively dry regions with little pr no rainfall and where the mantle is unprotected due to absence of vegetation.

16) What are Barchans?

The barchans are crescent or half moon shaped dunes of variable size. Their 'horns' point in the downward direction. Their height may vary from 15-200 mts. And width from a few to 1000s meter. They have a gentle windward slope and steeper leeward slope.

17) Define the terms

i) Focus

ii)  Epicenter

Focus:

The exact spot underneath the earth's surface,  at which an earthquake originates, is known as its focus.

Epicenter:

The earthquake then moves in the from of wave which are spread in all directions. These waves first reach the point at the surface, which is immediately above the focus or origin of the earthquake. This point is called epicenter.

18) What are the causes of earthquake?

The earthquake may be caused due to various reasons:

Earthquakes due to superficial movements.

Earthquake due to volcanic eruptions. Earthquake due to folding or faulting

19)           Define aquifer and the names the types of aquifers.

Groundwater occurs in permeable geologic formations is known as aquifers.i.e formations having structures hat permit appreciable water to move through them under ordinary field conditions.Aquifers may be classes as unconfined and confined, depending upon the presence or absence of a water table.

20) What do you understand by spheroidal weathering?

When weathering occurs, part of the disintegrated rock material is carried away by running water or any other transporting agent. Some of them are left on the surface of the bedrock as residual boulders. These boulders are then rounded off to spheroidal cores by the simultaneous attack of eroding agents on all sides. It is often seen that these boulders have an onion like structure. This kind of weathering is called spheroidal weathering.

21) Write short notes on:

*) Porosity

*) Permability

Porosity:

The portion of a rock or soil not occupied by solid mineral matter may be occupied by ground water. These spaces are known as voids, interstices, pores or pore space. The interstices can act as ground water conduits; they are characterized by their size, shape, irregularity, and distribution.

Permability:

The groundwater is stored in the pores of a rock and will hence be available in the groundrocks. The porosity of the rock, thus defining the maximum amount of water that can be stored in the rock. This is called permeability.

22) What is mean by water table?

The depth to upper surface of zone of saturation in free ground water is called water table. In other words, a static level of water in wells penetrating the zone of saturation is called water table.

23) What are the movements of the oceans?

There are three movements of oceans:

i)   Waves

ii)  Tides

iii) Currents.

Waves are only the rise and fall of water caused by the action of the winds. There is no movement forward. These are at the surface and not at great depth.

Currents are rivers in the sea. The water moves forward and falls at the depth as well. These are caused by the unequal temperature of equator and Polar Regions.

Tides are the rise and fall of seawater occurring twice in a lunar day.

24) Distinguish between magnitude and intensity of the earthquake.

Intensity of an earthquake may be defined as the ratio of an earthquake based on actual effects produced by the quakes on the earth.

Magnitude (M) of a tectonic earthquake may be defined as the rating of an earthquake based on the total mount of energy released when the over strained rocks suddenly rebound causing the earthquake.