
Volcán San Pedro (or Las Yeguas) (3,020 metres (9,908 ft)) is a stratovolcano on the shores of Lago de Atitlán, in the Sololá Department of northern Guatemala.
At its base is the village of San Pedro La Laguna.
Lake Atitlán (Spanish: Lago de Atitlán) is a lake in the Guatemalan Highlands of the Sierra Madre mountain range. It is in the Sololá Department of southwestern Guatemala. It is the deepest lake in Central America.
Atitlán means "between the waters". In the Nahuatl language, "atl" is the word for water, and "titlan" means between. The "tl" at the end of the word "atl" is dropped (because it is a grammatical suffix) and the words are combined to form "Atitlán".
The first volcanic activity in the region occurred about 11 million years ago, and since then the region has seen four separate episodes of volcanic growth and caldera collapse, the most recent of which began about 1.8 million years ago and culminated in the formation of the present caldera. The lake now fills a large part of the caldera, reaching depths of up to 340 m (1,120 ft).
The caldera-forming eruption is known as Los Chocoyos eruption and ejected up to 300 km3 (72 cu mi) of tephra. The enormous eruption dispersed ash over an area of some 6,000,000 square kilometres (2,300,000 sq mi): it has been detected from Florida to Ecuador, and can be used as a stratigraphic marker in both the Pacific and Atlantic oceans (known as Y-8 ash in marine deposits).[8] A chocoyo is a type of bird which is often found nesting in the relatively soft ash layer.
Since the end of Los Chocoyos, continuing volcanic activity has built three volcanoes in the caldera. Volcán Atitlán lies on the southern rim of the caldera, while Volcán San Pedro and Volcán Tolimán lie within the caldera. San Pedro is the oldest of the three and seems to have stopped erupting about 40,000 years ago. Tolimán began growing after San Pedro stopped erupting and probably remains active, although it has not erupted in historic times. Atitlán has developed almost entirely in the last 10,000 years and remains active, its most recent eruption having occurred in 1853.
On February 4, 1976, a very large earthquake (magnitude 7.5) struck Guatemala, killing more than 26,000 people. The earthquake fractured the lake bed and caused subsurface drainage from the lake, allowing the water level to drop two metres (6 ft 7 in) within one month.