THE ORIGEN OF ANDEAN VOLCANOES.

Tectonic pressures and volcanic activity gave shape the earth. The Andean Mountains were lifted up from the bottom of the Pacific Ocean.
The Andean mountain system is the result of global plate-tectonic forces during roughly the past 65 million years that built upon earlier geologic activity. About 250 million years ago the crustal plates constituting the Earth's land-mass were joined together into a super-continent. The subsequent breakup dispersed plates outward, where they began to take the form and position of the present-day continents. The collision or convergence of two of these plates -the continental South American Plate and the Oceanic Nazca Plate- gave rise to the mountain-building activity that produced the Andes mountain structures. The Andes host more volcanoes that have been active during the past 10,000 years than any other volcanic region in the world. The Andes also host the highest peaks in the Western Hemisphere. The highest of them is Mount Aconcagua (6959 meters/22,831ft) on the border of Argentina and Chile.
The prominent mountainous belt making up the Andean chain (Cordillera de los Andes) stretches approximately 8,900 kilometers (5,500mi) North to South from Venezuela to Patagonian Chile along the Western margin of South American continent. They separate a narrow Western coastal area from the rest of the continent, affecting deeply the conditions of life within the ranges themselves and in surrounding areas. They are not a single line of formidable peaks but rather a succession of parallel and transverse mountain ranges (cordilleras) and of intervening plateaus and depressions. Distinct Eastern (Cordillera Oriental) and Western (Cordillera Occidental) ranges are characteristic of most of the system. The directional trend of both ranges generally is North to South, but in several places the Eastern range bulges Eastward to form either isolated peninsula-like ranges or such high inter-montane plateau regions as the High Plateau (Altiplano), occupying adjoining parts of Argentina, Chile, Bolivia , and Peru. The Andes is also known as the "backbone" of South America.
The Andean Volcanism occurs within the Andean Volcanic Arc which is the Earth's longest but discontinuous continental-margin volcanic arc, along the Andes. It consists of 4 main distinct zones that are separated from each other by inactive volcanic gaps: -Northern, Central, Southern, and Austral.
-The Northern extends from Colombia to Ecuador. Of the volcanoes in this zone, 55 are in Ecuador, while 19 are in Colombia.
-The Central extends from Peru to Chile and forms the Western boundary of the High Plateau (Altiplano). There are 44 major and 18 minor volcanic centers that are considered to be active. Jaw-dropping details litter the landscape. It has been that way for over 10 million years. It has also been very dry weather in the area known as the Altiplano-Puna Plateau for at least a few millions years as well. It is the home of the Atacama Desert.
-The Southern extends roughly from Central Chile's Andes at Santiago to the Aysen Region, South of Chile.
-The Austral zone extends South of the Patagonian Volcanic Gap to Fire Land (Tierra del Fuego) archipelago.
The Andean volcanoes structure derive from the local geology (Nazca plate and Brazilian Shield).
The Pacific Ocean is being consumed here as much as 10 centimeters per year. The sub-duction zone is clearly seen as a deep trench off the coast. As the oceanic plate steeply subducts towards the mantle, it pushes the continental plate up and so has formed the second highest mountain chain on Earth.The sub-ducted plate melts easily at depth. In this process, it is rather helped by being well hydrated after millions of years underneath the Pacific Ocean; the water content reduces the melting temperature.The melt trickles up and collects in large magma chambers, which feed the many Andean volcanoes.The eruptions recycle both the oceanic crust and the Pacific water sub-ducted with it.
Another factor is the climate. The Andean mountains' climate is both wonderful and inhospitable. In the heights, the temperatures are mild, rarely cold, and most of the time clear sky. The cold Ocean currents keeps the climate dry; there are only a few months each year with some rain.
On the other side of the mountains begins a wetland, the Amazon and the Pantanal, where rain is a way of life, coloring the whole area in green. This way of life makes a tremendous contrast to the way of life in the West in which the dryness has formed a desert coloring the whole area in brown.
People live along the River Valleys and their agriculture is based on run-off from the high mountains.