<P> The northwestern part of the plateau is made up of lava flows or igneous rocks known as the Deccan Traps . The rocks are spread over the whole of Maharashtra and parts of Gujarat and Madhya Pradesh, thereby making it one of the largest volcanic provinces in the world . It consists of more than 2,000 metres (6,600 ft) of flat - lying basalt lava flows and covers an area of nearly 500,000 square kilometres (190,000 sq mi) in west - central India . Estimates of the original area covered by the lava flows are as high as 1,500,000 square kilometres (580,000 sq mi). The volume of basalt is estimated to be 511,000 cubic km . The thick dark soil (called regur) found here is suitable for cotton cultivation . </P> <P> The volcanic basalt beds of the Deccan were laid down in the massive Deccan Traps eruption, which occurred towards the end of the Cretaceous period between 67 and 66 million years ago . Some paleontologists speculate that this eruption may have accelerated the extinction of the dinosaurs . Layer after layer was formed by the volcanic activity that lasted many thousands of years, and when the volcanoes became extinct, they left a region of highlands with typically vast stretches of flat areas on top like a table. The volcanic hotspot that produced the Deccan traps is hypothesized to lie under the present day island of Réunion in the Indian Ocean . </P> <P> Typically the Deccan Plateau is made up of basalt extending up to Bhor Ghat near Karjat . This is an extrusive igneous rock . Also in certain sections of the region, we can find granite, which is an intrusive igneous rock . The difference between these two rock types is: basalt rock forms on eruption of lava, that is, on the surface (either out of a volcano, or through massive fissures--as in the Deccan basalts--in the ground), while granite forms deep within the Earth . Granite is a felsic rock, meaning it is rich in potassium feldspar and quartz . This composition is continental in origin (meaning it is the primary composition of the continental crust). Since it cooled relatively slowly, it has large visible crystals . Basalt, on the other hand, is mafic in composition--meaning it is rich in pyroxene and, in some cases, olivine, both of which are Mg - Fe rich minerals . Basalt is similar in composition to mantle rocks, indicating that it came from the mantle and did not mix with continental rocks . Basalt forms in areas that are spreading, whereas granite forms mostly in areas that are colliding . Since both rocks are found in the Deccan Plateau, it indicates two different environments of formation . </P> <P> The Deccan is rich in minerals . Primary mineral ores found in this region are mica and iron ore in the Chhota Nagpur region, and diamonds, gold and other metals in the Golconda region . </P>

How are the deccan rivers different from the northern rivers