Mojanda volcano

Volcán Mojanda is one of the largest volcanoes of Ecuador's northern Interandean Depression. It is located SW of the historic town of Otavalo. It is a twin volcano and consists of 2 neighboring active stratovolcanoes (Mojanda and Fuya Fuya).
Large-scale debris avalanches have occurred at both volcanoes.

Background:

Volcán Mojanda's geologic history is complex:
Remnants of an earlier stratovolcano edifice composed of andesitic lava flows underlies the present-day Mojanda edifice. The earlier volcano collapsed leaving a caldera, inside which a new smaller andesitic stratovolcano, Mojanda, was built. Mojanda consists mainly of basic andesite lava flows, scoria flow deposits and a thick summit series of vitric breccias. Mojanda's summit cone was destroyed by phreatoplinian eruptions which left a small summit caldera, containing 2 lakes.

The andesitic-to-rhyolitic Fuya Fuya volcano was constructed contemporaneously with Mojanda immediately to the west. Fuya Fuya had 2 major rhyolitic plinian eruptions, which might have been associated with the formation of a caldera, which occurred less than 165,000 years ago and left a large horseshoe-shaped caldera open to the west.
This collapse can be compared to Mount St. Helens 1980 debris avalanche. It removed a large part of Fuya Fuya and the western part of Mojanda volcano. The resulting avalanche was accompanied by large pyroclastic flows.
After this event, Fuya Fuya entered a more effusive eruptive phase and built a new cone and dacitic lava domes inside its caldera, including the San Bartolo cone. The youngest domes of Fuya Fuya are unglaciated and could be loess than 10,000 years old.

Sources:
- Smithsonian / GVP volcano information
- Robin et al (2009) "Evolution of the late Pleistocene Mojanda–Fuya Fuya volcanic complex (Ecuador), by progressive adakitic involvement in mantle magma sources", Bull Volc., Volume 71, Number 3, 233-25

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