Terrestrial heat and volcanism

Summary Although active volcanic territories are not characterised by extreme high heat flow, yet terrestrial heat is one of the main, if not hte first cause of volcanic activities. About 94 per cent of the known active volcanoes are in connection with orogenic zones including ocean ridges, which mean that processes responsible for the evolution of the continents cause the overwhelming majority of volcanism.There stages of the evolution of the continental crust can be distinguished: 1.) Growth of the continental cores by differentiation, 2.) Existence of peripheral growing zones around the first core, 3.) Intergrowth of the existing continents.Volcanism, as well as seismicity are manifestations of the evolution of the crust which is caused by the development of heat sources in the mantle. The heat partly melt the upper mantle and induce slow plastic flow in connection of differentiation. The space, left empty by continental uplift is filled by the slow plastic inflow of mantle from the ocean. This slow redistribution of mantle and curstal rocks disturbs the stress field, the rocks fail along the strained zones and zones of fractures appear sometimes with volcanic activity.