Natural Wonders [antikvár]

.1,1 mmm NTRODUCTION The earth's grandest illusion is that it appears never to change; a myth which has become embodied in our everyday language. 'As old as the hills', 'the everlasting sea', 'terra jirma' all embody the concept of a never-changing earth. True there are occasional dramatic and often devastating volcanic eruptions and earthquakes, but such events only ever affect a relatively small area of the earth's surface. The earth's secret is time. Spans of time which are measured not in hundreds of years, but in hundreds of thousands and millions of years. The most important agent in the moulding of the earth is water. Water, time and gravity together can achieve the impossible. As rain falls on the earth's surface, some of this weakly-acidic liquid eats its way into the rocks, gradually gouging out cracks and crevices. Percolating underground, it continues its work to create caves and caverns of immense size. Some of the rain runs directly off the surface into streams which unite to form mighty rivers thousands of miles long. Rivers are constantly eroding their own courses, removing vast quantities of rocks and sediment. In the upland areas, the main activity is directed The earth is full of contrasts. Below majestic waves, ideal for surfing, break on a Hawaiian shore. On the right is Mount Ama Dhablam in Nepal, one of the majestic peaks of the Himalayas.