Our Changing Earth

The lithosphere is broken into a number of plates, called lithospheric plates, which move very slowly, a few millimetres each year, because of the movement of molten magma inside the Earth. Forces acting from inside the Earth are endogenic forces, and those working on the surface are exogenic forces. Sudden endogenic movements cause earthquakes and volcanoes. The place inside the crust where an earthquake starts is the focus, the point on the surface directly above it is the epicentre, and earthquakes are measured with a seismograph on the Richter scale. The Bhuj earthquake in Gujarat on 26 January 2001 caused huge destruction. A volcano is a vent through which molten material erupts. Exogenic forces wear down and rebuild the land through weathering, erosion and deposition. Rivers form waterfalls, meanders, ox-bow lakes, floodplains, levees and deltas. Sea waves carve sea caves, arches, stacks and cliffs, and deposit sand to form beaches. Glaciers carve valleys and deposit moraines, while winds in deserts form mushroom rocks and sand dunes, and deposit fine loess, as in China.

Detailed Worksheet: Our Changing Earth Section A - Definitions (10 marks) 1. What are lithospheric plates? Why do they move? (2 marks) 2. Distinguish between endogenic and exogenic forces. (2 marks) 3. Define focus and epicentre of an earthquake. (2 marks) 4. What is a volcano? (2 marks) 5. What are weathering and erosion? (2 marks) Section B - Calculations and Applications (15 marks) 6. A lithospheric plate moves about 5 cm a year. (i) How far will it move in 100 years? (ii) In 1 million years (in km)? (iii) Why do we not notice this movement? (3 marks) 7. On the Richter scale, each whole number increase means about 10 times more ground shaking. How many times stronger is the shaking of an earthquake of magnitude 7 than one of magnitude 5? And magnitude 6 compared to 3? (3 marks) 8. Name the landform formed by: (i) river erosion where it falls over a steep slope (ii) a meander cut off from the main river (iii) river deposits at the mouth (iv) wind deposits in deserts (v) sea waves eroding through a headland (vi) glacier deposits. (3 marks) 9. The Bhuj earthquake occurred on 26 January 2001 at about 8:46 am IST. Convert this to GMT (IST is 5 hours 30 minutes ahead). How many years ago from 2026 did it occur? (3 marks) 10. Angel Falls in Venezuela is about 979 m high, and Jog Falls in Karnataka about 253 m. (i) Find the difference in height. (ii) About how many times higher is Angel Falls (to one decimal place)? (iii) How are waterfalls formed? (3 marks) Section C - Diagrams (10 marks) 11. Draw labelled diagrams showing the formation of a meander and an ox-bow lake. (4 marks) 12. Draw a labelled diagram of an earthquake showing the focus, epicentre and seismic waves. (3 marks) 13. Draw labelled sketches of a sea arch, a sea stack and a mushroom rock. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. (i) List three safety measures to be taken during an earthquake. (ii) Why do buildings collapse in earthquakes? (iii) How can buildings be made earthquake-resistant? (iv) Why can't earthquakes be predicted accurately? (v) Name one earthquake-prone region of India. (5 marks) 15. A river flows from mountains to the sea. (i) Name two landforms formed in the mountains. (ii) Name two formed in the plains. (iii) Name one formed at the mouth. (iv) Why do deltas have very fertile soil? (5 marks) 16. In deserts, rocks are often shaped like mushrooms and sand forms hills. (i) Why is the lower part of a mushroom rock narrow? (ii) What are sand dunes? (iii) What is loess? (iv) Why are the effects of wind greater in deserts? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Draw labelled diagrams for landforms and show arrows for the direction of movement.