It is slow because rocks flow like thick treacle. Rock is pushed up like a bow wave in front of a boat as one tectonic plate pushes into another. Satellite techniques show that the central peaks of the Andes and Himalayas are rising. The outer peaks are sinking as the rock flows slowly away from the ‘bow wave Mountain-building is very active during orogenic (mountain-forming) phases that last millions of years.


Different orogenic phases occur in different places, for example the Alpine, Caledonian, Hercynian in Europe and the Huronian, Nevadian and Pasadenian in North America. The Caledonian was about 550 million years ago. Mountain-building makes the Earth’s crust especially thick under mountains, giving them very deep ‘roots’. 
 "As mountains are worn down, their weight reduces and the ‘roots’ float upwards. This is called isostasy". A few high mountains are lone volcanoes, such as Africa’s Kilimanjaro, which are built by many eruptions. Some volcanic mountains are in chains in volcanic arcs , such as Japan’s Fujiyama. 
 Most high mountains are part of great mountain ranges stretching over hundreds of kilometres. Some mountain ranges are huge slabs of rock called fault blocks . They were forced up by quakes. The biggest mountain ranges, such as the Himalayas and the Andes, are fold mountain ranges. 

The height of mountains used to be measured from the ground, using levels and sighting devices to measure angles. Now mountains are measured more accurately using satellite techniques. Satellite measurements in 1999 raised the height of the world’s highest peak, Mt Everest in Nepal in the Himalayas, from 8848 m to 8850 m. All 14 of the world’s peaks over 8000 m are in the Himalayas - in Nepal, China and Kashmir. 
Temperatures drop 0.6°C for every 100 m you climb, so mountain peaks are very cold and often covered with ice. The air is thinner on mountains, so the air pressure is lower. Climbers may need oxygen masks to breathe. 

Caves in mountains 


Caves are giant holes that run horizontally underground. Holes that plunge vertically are called potholes. 
The most spectacular caves, called caverns, are found in limestone. Acid rainwater trickles through cracks in the rock and wears away huge cavities. 

The world's largest cave

 The world’s largest known single cave is the Sarawak Chamber in Gunung Mulu in Sarawak, Malaysia. 

The longest cave of world

The longest cave system is the Mammoth Cave in Kentucky,USA, which is 560 km long. Many caverns contain fantastic deposits called speleothems. They are made mainly from calcium carbonate deposited by water trickling through the cave. 
Stalactites are icicle-like speleothems that hang from cave ceilings. Stalagmites poke upwards from the floor. The world’s longest stalactite is 6.2 m long. It is in the Poll an Ionain in County Clare, Ireland. The world’s tallest column is the Flying Dragon Pillar in the Nine Dragons Cave, Guizhou, China.

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