LAKES AND GROUNDWATER FACTS

 Natural lake occur where a large quantity of water collects in a hollow in impermeable rock, or is prevented from draining away by a harrier, such as moraine or solidified lava. lakes are often relatively short-lived landscape features, as they tend to become silted up by sediment from the streams and rivers that feed them. Some of the more long-lasting lakes are found in deep rift valleys formed by vertical movements of the Earth's crust - for example, Lake Baikal in Russia, the world's largest freshwater lake and the Dead Sea in the Middle East, one of the world's saltiest lakes. Where waters is able to drain away, in sinks into the ground until it reaches a layer of impermeable rock, then accumulates in the permeable rock, then accumulates in the permeable rock above it, this water - saturated permeable rock is called an aquifer. The saturated zone varies in depth according to seasonal and climatic changes. In wet conditions, the water stored underground builds up, while in dry periods it becomes depleted. Where the upper edge of the saturated zone- the water table- meets the grounds surface, water emerges as springs. In an artesian basin, where the aquifer is below an aquiclude, the water table throughout the basin in determined by its height at the rain. In the Centre of such a basin, the water table is above ground level. The water in the basin is thus trapped below the water table is above ground level. The water in the basin is thus trapped below the water table and can rise under its own pressure along fault lines  or well shafts. 

Furthermore, Coastlines are among the most rapidly changing landscape features. Some are eroded by waves, wind, and rain, causing cliffs to be undercut and caves to be hollowed out of solid rock. Others are built by waves transporting sand and small rocks in a process known as longshore drift, and by rivers depositing sediments in deltas. Additional influences include the activities of living organisms such a coral, crustal movements, and sea-level creates an emergent coastline, with cliffs and beaches stranded above the new shoreline. sinking land or a rise in a sea level produces a drowned coastlines, typified by fjrods or submerged river valleys.