What is a spring?
Many types of rock contain tiny holes like a sponge, in which rainwater collects. The water gradually sinks down and eventually flows out lower down. Water stored in such porous rocks sometimes bubbles to the surface in springs. They are usually found near the foot of hills. Spring water is often used for drinking because as it passes through rock, any harmful substances or germs are filtered out. On more level ground, spring water is found by digging a well to reach the underground water. Small outflows of water can lead to the formation of isolated bogs or marshes.
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How is limestone caves formed?
Water can actually dissolve certain types of rock, eventually forming underground streams and caves.
Carbon dioxide in the air dissolves in rainwater to form a very weak acid, which can slowly dissolve soft limestone rock. Over thousands of years, water seeping into cracks in limestone rock dissolves so much that the cracks become holes. Slowly the holes grow even larger and form caves. These may be many kilometres in length and very deep. Sometimes the roofs of huge caves collapse, forming narrow valleys or gorges.
Picture credit: google