Gravity Spring. If the underground water appears as a spring on the land surface, the springs are known as gravity springs. The water of such springs flows from higher to lower level under the force of gravitation. If the water of the springs comes from a place, which has a high temperature, the springs are called Hot Springs. Sometimes the water of springs passes over such rocks, which are rich in minerals. The water of such springs has a high amount of minerals in solution. Such springs are known as mineral springs. The hot springs are found at Tata Pani (Simla). Sometimes the hot and minerals springs have been found useful in the cure of many skin diseases. At some places the hot gases of volcanic lava heat the underground water so much that the water begins to boil. Such springs having boiling water are called Boiling Springs. Sometimes, the spring water contains iron particles in oxidized form. This makes the water of the spring yellow or red. Algae, a vegetation, grows better in the warm water of springs.
Geyser. Geysers are springs of hot water, which expel water vigorously at intervals. The interval depends upon the particular nature of the spring. The geysers are less common than ordinary springs and are usually found in Iceland, New Zealand, USA. (Yellowstone Park), etc.
Artesian Wells. It has been found in some desert areas that water comes out from some hole or crack while the surrounding areas is dry and has dry sand all around. The water comes out like a fountain. Such wells are called Artesian Wells and are not limited to desert areas. In fact, Artesian wells receive their name from Artois which is a province of France where such wells abound. The first artesian well was dug at Calais (France).
The work of underground water
The rate of flow of underground water is very low. As it moves slowly, the solution work done by it is more important. Hence the erosion and deposition effected is the most important aspect of underground water.
The underground water does not dissolve all rocks at the same rate. The limestone rocks are most readily dissolved. Other rocks which are affected by solution process are Dolomite, Gypsum, Chalk, etc.
The rain water while passing through the air dissolves carbon dioxide gas present in the atmosphere. This rain water which has carbon dioxide dissolved in it becomes weakly acidic and can dissolve Limestone rocks. When this water charged with carbon dioxide flows in the soil, it also receives carbon dioxide produced the bacteria of the soil. This increases the dissolving power of the rain water to a great extent.
This water dissolves many minerals and produces many chemical salts. Mostly these are the Chlorides, Sulphates and Calcium, Magnesium, Sodium, Potassium, Iron, etc. These salts of Calcium and Magnesium when dissolved in water make it hard. This water is known as Hard Water.