Gate 2011 1.9

1.9 The depositional feature that forms where a stream emerges from a mountainous region onto a plain is called

(A) alluvial fan

(B) natural levee. 

(C) delta

(D) point bar

Alluvial Fans. The alluvial material which flows down from

mountains accumulates at foothills where the stream enters a plain. The deposition occurs due to abrupt change in the gradient of the river valley. Such deposits spread out in the shape of flat fans and are called “alluvial fans”. Usually, the coarse material is dropped near the base of the slope while finer material is carried further out on the plain. Alluvial fans form many adjacent streams along a mountain that may merge to form a long wedge of sediment called “alluvial aprons”.

Deltas. These are submerged equivalents of alluvial fans. “Deltas” are deposits built at the mouths of streams. The deltas are usually triangular in shape with their apex pointed upstream. When a stream enters an ocean or lake, the currents of the flowing water dissipate quickly. This results in the deposition of the series of sedimentary layers which make up the delta. The material of most deltas is well sorted and many deltas are uniformly graded. The structure of a delta deposit is shown

Point Bars. In meandering rivers, sediment deposits occur as point bars. The “point bars” are the crescent-shaped deposits which occur at inside bends of a river channel.

Natural Levees. “Natural levees” are the low ridges which are formed on both sides of a river channel by the accumulation of sediment. They tend to confine the flow of river water into its channel between flood stages. The natural levees occur in rivers which have broad flood plains. During floods, the river overflows its bank and its velocity decreases rapidly. As a result most of the coarse sediment is deposited along the area bordering the river channel and finer sediments are deposited more widely over the flood plain. In this way, successive floods build up ridges on both sides of a river channel, which are called “natural levees. 

Gate 2011 1.8

1.8 The planet which contributes maximum to the angular momentum of the solar system is

(A) Earth

(B) Mars

(C) Jupiter

(D) Saturn

    98% of the angular momentum is concentrated in the planets and the remaining 2% is present in the sun. In other words, the sun does not rotate fast enough. 

Jupiter is by far the largest of the planets in the solar system. Its mass is 318 times of that of Earth hence contributes maximum to the angular momentum of the solar system as it is proportional to the mass of the body.

Gate 2011 1.7

1.7 Tsunamis are

(A) gravity waves

(C) Capillary waves

(D) internal waves

(B) acoustic waves

Tsunami: When the ocean floor is abruptely lifted droppped by a submarine earthquake or land slides the entire water column is pushed up and down more than 95% of the potential energy of displaced water is gravitational and less than 5% is elastic energy resulting from compression of ocean floor and water column. The potential energy of the vertical motion is converted to kinetic energy and propogates away from the source as a tsunami

    In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium.  A gravity wave results when fluid is displaced from a position of equilibrium. The restoration of the fluid to equilibrium will produce a movement of the fluid back and forth, called a wave orbit. Gravity waves on an air–sea interface of the ocean are called surface gravity waves or surface waves, while gravity waves that are within the body of the water (such as between parts of different densities) are called internal waves. 

    Wind-generated waves on the water surface are examples of gravity waves, as are tsunamis and ocean tides.

    Wind-generated gravity waves on the free surface of the Earth's ponds, lakes, seas and oceans have a period of between 0.3 and 30 seconds (frequency between 3.3 Hz and 33 mHz).

Gate 2011 1.6

1.6 The deflection of ocean currents in the northern and southern hemispheres is due to

(A) thermohaline circulation 

(B) Coriolis effect

(C) El Nino effect 

(D) monsoon effect

Coriolis Effect It intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere. These large accumulations of water and the flow around them are called ‘Gyres’. These produce larger

circular currents in all the ocean basins

Gate 2011 1.5

1.5  Which of the following statements is TRUE for the temperature variation with altitude in the earth's atmosphere?

(A) Temperature increases in both stratosphere and mesosphere

(B) Temperature decreases in stratosphere and increases in mesosphere

(C) Temperature increases in stratosphere and decreases in mesosphere

(D) Temperature decreases in both stratosphere and mesosphere

Troposphere : Temperature decreases with altitude.

stratosphere : Temperature increases with altitude.

Mesosphere : Temperature decreases with altitude.

Thermosphere : Temperature increase with altitude.

Gate 2011 1.4

1.4 Variation of the geomagnetic field observed over the last 500 years indicates that the dipole moment of earth's the magnetic field has been

(A) decreasing

(B) increasing

(C) constant

(D) fluctuating randomly

Measurements taken from 1835 to 1965 reveal that the earth lost a whopping 8% in its magnetic field strength over those 130 years.) More recent measurements confirm this exponential rate of decrease, at a rate of about 1.5% every 30 years.) That means if you are 60 years old, in your own lifetime, the earth’s magnetic field decreased in strength by about 3%. 

When we look at the other planets of the Solar System, we find the same thing occurring. Our moon and Mars, for instance, used to have strong fields, but their fields have already died out, just like the earth’s is on the path to doing. 

When our probes visited Mercury (in 1975), not only did we discover it does have a field, on subsequent visits from our probes (up to 2011), we found its field is also exponentially decaying as well. So from 1975 to 2011, Mercury’s field decreased 7.8% in strength! 

One of the most awesome discoveries in all of this is that not only is the earth’s field decaying, but it is doing so at a precise exponential linear rate of decay. Not only that, but we have found a ‘little wobble’ (a precise sinusoid oscillation) in this rate of decay that further strongly implies “the cause of the decay is energy dissipation,” which is a death-knell to the old-earth dynamo model, which in turn means the earth is young:

Gate 2011 1.3

1.3 The P-wave velocity of the earth’s mantle at the Mohorovicic discontinuity is

 (A) 5.5 km/s 

(B) 6.0 km/s 

(C) 7.0 km/s

(D) 8.0 km/s 

The Moho is the boundary between the crust and the mantle in the earth.

 The boundary is between 25 and 60 km deep beneath the continents and between 5 and 8 km deep beneath the ocean floor.

Typical values for P-wave velocity in earthquakes are in the range 5 to 8 km/s. The precise speed varies according to the region of the Earth's interior, from less than 6 km/s in the Earth's crust to 13.5 km/s in the lower mantle, and 11 km/s through the inner core.

2011 1.2

1.2 Which of the following rocks contributes to the highest amount of radioactive heat in the earth’s crust?

(A) basalt

(B) gabbro

(C) dunite

(D) Granite

GRANITE: It mainly consists of a larger part of earth crust and mostly contain alkali feldspar (K- felds part) & Quartz with small amount of other accessory minerals Since K (potassium) is a radioactive element because of its hight abundancy contributes to the highest amount of radioactive heat in the earth crust

Gate 2011 1.1

1.1 The increase in the length of a day on the earth at a rate of 2.4 milliseconds/100 years is due to

(A) prolate tidal bulge

(C) spring tide

(B) tidal friction

(D) bodily earth tide

Prolate Tidal Bulge: For large astronomical bodies that are nearly spherical due to self gravitation the tidal distortion produces a slightly prolate spheroid i.e. an axially symmetric ellipsoid that is elongated along its major axis.

Tidal friction: The tidal friction of the earth is manifested in a gradual increase in the length of the day. The effect is very small. Tidal theory predicts an increase in the length of the day of only 2.4 millisecond per century.

Spring Tide: The unusually high tides at opposition (when the full moon is on the opposite side of the earth from the sun) and conjunction (The new Moon is on the same side of the earth from the sun) are called spring tides.

Bodily Earth tide: The tidal deformation corresponds to a redistribution of mass, which modifies the gravitational potential of the Earth and augments the elevation

of the free surface called bodily earth tides

  So why is Earth's rotation slowing down in the first place? A large part of it is due to something called tidal braking, which basically means that the Moon's tidal pull is acting as a drag on our planet. "The heaping up of water drags on Earth as it spins underneath,“

    Incidentally, as our spin slows down, the Moon's orbit is also growing by around 4 cm a year. But that's not the only factor involved - the world's sea levels, as well as electromagnetic forces between Earth's core and its mantle, have an effect on Earth's spin too, which is why it's so unpredictable.

    One example of this is that ice ages slow the planet's rotation down by freezing all the water in the poles, causing the planet to squish slightly and spin more languidly, just like an ice skater when she puts her arms wide.

What two motions do all planets have?

    That the Moon keeps the same part of its surface always turned toward Earth is attributed to the past effects of tidal friction in the Moon. The theory of tidal friction was first developed mathematically after 1879 by the English astronomer George Darwin (1845–1912), son of the naturalist Charles Darwin.

    Tidal friction, in astronomy, the strain produced in a celestial body (such as the Earth or Moon) that undergoes cyclic variations in gravitational attraction as it orbits, or is orbited by, a second body. Friction occurs between water tides and sea bottoms, particularly where the sea is relatively shallow, or between parts of the solid crust of planet or satellite that move against each other. Tidal friction on the Earth prevents the tidal bulge, which is raised in Earth’s seas and crust by the Moon’s pull, from staying directly under the Moon. Instead, the bulge is carried out from directly under the Moon by the rotation of the Earth, which spins almost 30 times for every time the Moon revolves in its orbit. The mutual attraction between the Moon and the material in the bulge tends to accelerate the Moon in its orbit, thereby moving the Moon farther from Earth by about three centimeters (1.2 inches) per year, and to slow Earth’s daily rotation by a small fraction of a second per year. Millions of years from now these effects may cause the Earth to keep the same face always turned to a distant Moon and to rotate once in a day about 50 times longer than the present one and equal to the month of that time. This condition probably will not be stable, due to the tidal effects of the Sun on the Earth-Moon system.

Gate 1997 1.2

Gate 1997

1.2 The vernal equinox occurs on

(A) March 21   

(B) June 21   

(C) September 21

(D) December21

A) March 21

Equinox: The Sun is exactly above the Equator and day and night are of equal length, An equinox occurs twice a year, around 21 march and 23 September,

At equinox the sun is at one of the two opposites points on the celestial sphere where the celestial equator and ecliptic intersect. These point of intersection are called equinoctial points. Classically these vernal point and the autumnal point.

In the Northern Hemisphere, the vernal equinox falls about March 20 or 21, as the Sun crosses the celestial equator going north. In the Southern Hemisphere, the equinox occurs on September 22 or 23, when the Sun moves south across the celestial equator. According to the astronomical definition of the seasons, the vernal equinox also marks the beginning of spring, which lasts until the summer solstice (June 20 or 21 in the Northern Hemisphere, December 21 or 22 in the Southern Hemisphere).

Gate 1997-1.1

Gate 1997

1.1 A semipermeable layer that yields water slowly in comparison to the adjoining aquifer is called an

(A) aquiclude
(B) aquifer

(C) aquitard
(D) aquifuge

(C) Aquitard

    An aquitard is a zone within the Earth that restricts the flow of groundwater from one aquifer to another. 

Aquitards comprise layers of either clay or non-porous rock with low hydraulic conductivity.

A completely impermeable layer  is called an aquiclude or aquifuge.