Colachi - Acamarachi Complex
Colachi and Acamarachi are two distinct cones
about 6 km apart which are the most conspicuous
elements of a small volcanic complex. Acamarachi
(6046 m) is the highest peak in the region and is a
simple symmetrical cone conspicuous from the
ground for the extremely steep slopes near its
summit; angles of ~45° have been measured on
steeply dipping lava flow remnants. A poorly
preserved summit crater is present and the lack of
any morphologically distinct lava flows on the flanks
suggest that it was largely constructed in pre-
Holocene times, but the summit lava flows may be young. A large dome is present on its
northern side, upsetting the symmetry of the volcano. Colachi is a similar but smaller
symmetrical cone, with a degraded summit crater and some recognisable flow features,
especially on its eastern flank and in the summit region. Although these two cones are two of
the loftiest peaks in the area, they are actually relatively small edifices with heights of ~800 -
1200 m above their base level of ~4,800 m. Preliminary mapping indicates that they are built on
a large uplifted block of welded ignimbrites, possibly the resurgent center to an older caldera.
The most recent activity in the Colachi-Acamarachi complex has been the eruption of a pair of
small silicic flows or coulées. The largest of these covers ~7 km and occupies the saddle
between the two volcanoes, and there is a smaller one (~3 sq km) at the western foot of
Colachi. These are typically glassy and have the conspicuous flow ridged morphology of other
silicic flows of the region. There no records of historic eruptions.
Summit Elevation: 5631 m (Colachi)
Latitude: 23.30°S
Longitude: 67.62°W
Summit Elevation: 6046 m (Acamarachi)
Latitude: 23.30° S
Longitude: 67.616° W
click on the pictures to enlarge
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about 6 km apart which are the most conspicuous
elements of a small volcanic complex. Acamarachi
(6046 m) is the highest peak in the region and is a
simple symmetrical cone conspicuous from the
ground for the extremely steep slopes near its
summit; angles of ~45° have been measured on
steeply dipping lava flow remnants. A poorly
preserved summit crater is present and the lack of
any morphologically distinct lava flows on the flanks
suggest that it was largely constructed in pre-
Holocene times, but the summit lava flows may be young. A large dome is present on its
northern side, upsetting the symmetry of the volcano. Colachi is a similar but smaller
symmetrical cone, with a degraded summit crater and some recognisable flow features,
especially on its eastern flank and in the summit region. Although these two cones are two of
the loftiest peaks in the area, they are actually relatively small edifices with heights of ~800 -
1200 m above their base level of ~4,800 m. Preliminary mapping indicates that they are built on
a large uplifted block of welded ignimbrites, possibly the resurgent center to an older caldera.
The most recent activity in the Colachi-Acamarachi complex has been the eruption of a pair of
small silicic flows or coulées. The largest of these covers ~7 km and occupies the saddle
between the two volcanoes, and there is a smaller one (~3 sq km) at the western foot of
Colachi. These are typically glassy and have the conspicuous flow ridged morphology of other
silicic flows of the region. There no records of historic eruptions.
Summit Elevation: 5631 m (Colachi)
Latitude: 23.30°S
Longitude: 67.62°W
Summit Elevation: 6046 m (Acamarachi)
Latitude: 23.30° S
Longitude: 67.616° W
click on the pictures to enlarge
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