Relief - the difference in altitude between the high and the low parts of a land surtace. Ravine - a cleft or cut in the Earth's surtace. When a stream runs down a mountain, it cuts a ravine. Index Contour - every fifth line on a topographic map is darker and has a number written on it. These lines are the index contours.
Environmental issues evolve as people interact with and change the physical geography of the planet.
Many of these issues facing the planet today are related to the interaction of the twentieth century technologies, population growth and other environmenal factors. You will need to make some clay mountains and find out what their contour lines look like. First, soften the clay with your hands and form it into a little mountain about three inches high. Hold the ruler upright in the pan so that 0 inches is at the bottom. Ask someone to pour water into the tub or pan until the water level is at exactly 1l2 inch.