Sumaco

Geography & Climate

Sumaco is located in Ecuador, within the Northern Andean Volcanic Arc of the broader South America Volcanic Regions. Situated at 0.54° S, 77.63° W in the Southern Hemisphere, the volcano lies within a tropical climate zone. Standing at 3,990 meters above sea level, Sumaco towers above the alpine zone, where vegetation gives way to bare rock, snow, and ice for much of the year. The high elevation means the upper slopes experience significantly colder temperatures than surrounding lowlands. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Sumaco sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Ecuador near Sumaco, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is trachybasalt / tephrite basanite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Sumaco has 3 recorded eruptions in the geological database, spanning from 1650 CE to 1933 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1650 CE, reaching VEI 3 on the Volcanic Explosivity Index. These eruptions span roughly 283 years of volcanic history. The most recent eruption in 1933 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 3, Sumaco has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel.

GVP Reference Summary

The forested Sumaco stratovolcano rises above the jungles of the western Amazon basin, east of Antisana volcano, and occupies an isolated position far to the east of the main Andes volcanic axis. Constructed over Cretaceous sedimentary rocks, it forms a relatively symmetrical cone in an area of heavy rainfall and erosion. Sumaco has produced alkaline tephritic, basanitic, and phonolitic rocks distinct from those of the main Andean chain. The volcano has a broad summit crater, 300 x 400 m wide, containing a central cone. Reports of historical eruptions are somewhat ambiguous; an eruption is inferred in the 18th or early-19th century on the basis of changes in crater morphology.

— Smithsonian Institution, Global Volcanism Program