OUR CHANGING EARTH
Q1.How are ox-bow lakes formed?Explain with the help of diagram.
A1.(i)When the rivers entres the plains its speed reduces and forms large bends
called meanders.
(ii)Speed of the river is higher on the outside of the bend and hence erodes the
land surface.
(iii)The river is slow on the inside of the bend,so it leaves the eroded material
there.
(iv)Due to this process the bends becomes wider and closer to each other and
gradually join to form a single stream of water.
(v)At this stage a meander gets cut-off completely from a main river and dries up
gradually due to zero supply of water.
(vi)These separated meanders are called ox-bow lakes.
Q2.Describe the erosional and depositional features of the glaciers.
A2.(i)Glaciers slide down from the high mountain slopes.
(ii)They erode the mountains and carry rock pieces along.
(iii)In this process they carve out deep U-shaped valleys.
(iv)When the ice melts,this valley gets filled with water to form beautiful lakes.
(v)The eroded rock pieces and sediments get deposited in these valleys forming
glacial morains.
Q3.How are benches formed?
A3.The river waves carry the eroded pebbles ,gravels and sand to the coast and
form benches.
Eg:Marina Bench in Chennai.
Q4.What are sand dunes?How are they formed?
A4.(i)Sand dunes are low hill like structures made of sand in the deserts.
(ii)When the wind in the desert stops blowing it drops the coarse sand particles at
one place.
(iii)Sand dunes keep changing their shape and place.
Q5.Differentiate between exogenic and endogenic forces?
A5.
Exogenic
a)These are forces which originate and
work on the surface of the earth
b)They lead to the erosion and
deposition of the landforms with the
help of wind,water and ice.
Eg:Sea waves,rivers
Endogenic
These are forces which originate and
act in the interior of the earth
They lead to sudden changes on the
earth surface like earthquakes and
volcanoes and sometimes slow changes
like formation of mountains eg:
volcanoes,earthquekes
Q6.How is delta formed?
A6.(i)When the river approaches the sea,it becomes very slow.
(ii)It is carrying a large amount of silt.
(iii)Here it starts breaking into number of small streams called distributaries.
(iv)All the sediments or silt is collected here.
(v)At the mouth of the river a triangular shaped land is formed which is called
delta.
Eg:Sunderbans delta.
Q7.Name the three types of earthquakes (scismic )waves.
A7.(i)P waves or longitudinal waves
(ii)S waves or transverse waves
(iii) L waves or surface waves.
Q8.Enlist the erosional and depositional features of the sea waves.
A8.(a)The erosion and deposition of sea waves giverise to coastal landforms.
(b)Sea waves continuously strick at the rocks.
(c)Cracks develop over time they become larger and wider.
(d)Thus,hollow like caves are formed on the rocks.These are called sea waves.
(e)As these cavities become bigger and bigger only the roof of the caves
remain,thus forming sea arches.
(f)Further erosion breaks the roof and only walls are left.These walls like featues
are called stacks.
(g)The steep rocky coast rising vertically sea water is called sea cliff.
(h)The sea waves deposite sediments along the shores forming benches.
Q9.How are flood plains formed?
A9.(i)At times the river overflows its banks.
(ii)This leads to flooding of neighbouring areas.
(iii)As it floods it deposits layers of soil and other material called sediments along
its banks.
(iv)This leads to the formation of flat fertile floodplain.
Q10.Give Reasons:
(i)Some rocks take the shope of a mushroom:In the desert winds erodes lower
section of the rock more than the upper part.Therefore such rocks have a
narrower base and wider tops.Such rocks are called mushroom rocks.
(ii)Flood plains are very fertile:
(a)During floods river overflows their banks.
(b)This results in the flooding of neighbouring areas.
(c)When water floods the silt and other materials brought by floods remain there.
(d)Due to spread of new silt the floodplain are fertile.
Q11.What is an Earthquake?Define focus and epicenter.
A11. (i)When the lithospheric plates moves the surface of the earth vivrates.
(ii)These vibrations can travel all around the earth are called earthquakes.
Focus:The place in the crust where the movement starts is called focus.
Epicentre:The place on the surface above the focus is called epicenter.