Cotopaxi

Cotopaxi is the sight to behold. Towering above the neighboring Andean peaks in north-central Ecuador, South America, it is an almost perfectly symmetrical volcanic cone. Dominating the capital city of Quito skyline to the south, 19,348 feet in elevation, Cotopaxi is the second highest peak in the Ecuador and the highest continually active volcano in the world. Its flanks are largely covered by permanent fields of snow and ice. And it is the snow that presents the greatest peril when the volcano intermittently erupts. Cotopaxi means "Smooth Neck of the Moon" and the native people have worshiped the mountain for centuries.
Cotopaxi's shapely profile was a long time in the making, for it is actually composed of two volcanic structures, with the newer one superimposed on its ancient ancestor. The older volcano called Picacho, was formed long before any of the neighboring extinct volcanoes in this area of the Andes. Traces of its caldera (a giant crater like cavity formed when a volcano's top collapses in an explosion.) are still visible on Cotopaxi's flanks. 

Cotopaxi is known as a Stratovolcano: built up with lava flows alternating with layers of ash and other volcanic materials that were exploded from its vent. But the most deadliest effects of its eruptions result from Lahars - gigantic avalanches of mud and meltwater that periodically come flooding down its flanks. The first recorded eruption of Cotopaxi was in 1533. Of the many that have occurred since then, the worst took place in 1877. The explosions were heard over a radius of more than 200 miles, clouds of ash and pumice completely darkened the midday sky and the accompanying lahars killed thousands of people. Evidence of that catastrophic flow can still be seen throughout much of the countryside of the Sierras. Though Cotopaxi remains active, it has been long since the last large eruption.