The 1.98 Ma Laguna Colorada ignimbrite shield lies between the Pastos Grandes and Guacha calderas. Most large ignimbrite eruptions coincide with caldera collapse like at Pastos Grandes and Guacha. However, the Laguna Colorada ignimbrite does not have an apparent associated collapse caldera. Instead, the ignimbrite takes on a shield-type morphology, with effusive lava domes erupting from the apex of the shield covering any evidence for collapse.
The Laguna Colorada ignimbrite is easily accessed thanks to its namesake--Laguna Colorada--lying at the edge of the western slope of the ignimbrite shield. The Sol de Mañana geyser fields and Volcan Uturuncu are also nearby. The small towns of Huayajara on the southern edge of the lake and Quetena near the base of Uturuncu are lovely places to spend the night.
The above map shows the major roads through Laguna Colorada. Pink indicates the extent of the ignimbrite. The blue outlines the lava domes.
The small town of Quetena was our home base while working on Laguna Colorada and Guacha. Despite its remoteness, Quetena does have two nice hostels and many llamas.
Our breakfast table had very nice table cloths!
Huayajara is a tiny town on the southern end of Laguna Colorada. Most of the buildings are hostels as it is a tourist town built for Laguna Colorada visitors. We only spent one night in Huayajara, but it was enough for us to meet the town's Legless Llama!
The Laguna Colorada ignimbrite defines the boundaries of the ignimbrite shield and can be observed in many places. The best outcrops, however, are along the northern road from Laguna Colorada to Quetena at 22°13'20.17"S 67°24'49 .03"W and just off the southern road west of Quetena Grande near 22°21'27.29"S 67°23'53.27"W.
The Laguna Colorada ignimbrite is a fairly typical ignimbrite for the APVC. The dominant mineralogy consists of plagioclase, quartz, biotite, and amphibole. Small lithic and pumice fragments are common throughout the ignimbrite, although their concentrations vary depending on location.
Lithic fragments—mostly consisting of juvenile material—are common throughout the ignimbrite and are incredibly abundant in some facies such as this one. Pumice fragments are small for the most part, with some larger pumice concentrated near the base of the ignimbrite.
The ignimbrite is highly welded near the domes. Welding often occurs due to high temperatures and large volumes of ignimbrite erupted near the vent. The welded blocks in this picture contain small fiamme, indicating compaction. You can see the welded ignimbrite in several locations on the northern road, particularly on one of several sharp curves near 22°13'5.09"S 67°26'6.72"W.
Effusive dacitic domes erupted after the ignimbrite emplacement cover the center and extend down the southern edge of the Laguna Colorada shield. The youngest domes appear to be in the center of the shield. The central domes show heavy hydrothermal alteration. You can see spectacular panoramas of the domes looking north across the Salar de Chalviri from Puripica Chico, as seen in the above picture. A road following the western edge of the lava domes connects the northern and southern roads and offers panoramic views of Laguna Colorada.
At ignimbrite shields, lava domes erupt after the ignimbrite is emplaced and cover any evidence for collapse near the vent. This greatly complicates things and scientists are left to find creative methods of studying vent regions of ignimbrite shields. For example, volcanologists at the Cerro Panizos shield have used the orientation of magnetic crystals to observe collapse structures.
One of the most unusual features about the Laguna Colorada ignimbrite shield is a layer of dacite disks found associated with the ignimbrite. These disks are crystalline and have been flattened, forming round, pancake-like shapes. Their emplacement mechanism is unknown. In the APVC these disks appear to be unique to Laguna Colorada. They are found in abundance on the western and southeastern sides of the ignimbrite but are not found near welded material. The best places to observe these disks are off the northern and western roads at 22°10'32.27"S 67°42'11.48"W and 22°16'59.23"S 67°43'17.18"W.
Many of the disks are up to 1/2 meter long. All are flattened to some extent, although aspect ratios can vary in an outcrop such as this. Many of the disks appear to have flowed like viscous lavas during emplacement. In outcrops, the disks are encased in a fine ash.
The disks can even be used as frisbees, although we wouldn't recommend a game of ultimate at this elevation!
The Laguna Colorada ignimbrite shield is named after the Laguna Colorada salt lake on its western edge. Laguna Colorada is a vibrantly red lake with islands of white borax. Algae and sediments give Laguna Colorada its red color.
Flamingos and tourist frequent its waters and the nearby village of Huayajara.
From the ignimbrite shield you are treated with an excellent view of the lake.
Sol de Mañana is an active geothermal field to the southwest of the Laguna Coloradaignimbrite shield. It is reminiscent of a small Yellowstone, complete with bubbling mud pots, geysers, and the acrid smell of sulfur. Unlike Yellowstone, however, there are no boardwalks. You are free to walk wherever you wish around this geothermal field but be careful!! The crust is thin and one false step can send you into boiling mud!
Sol de Mañana is one of two geothermal areas in the APVC. The other is El Tatio in Chile.
Boiling mud produces interesting patterns such as this radial star shape.
Geothermal fields are proof that a magma body still resides in the crust under the APVC.
Volcán Uturuncu is a 19,711 ft (6008 m) stratovolcano to the east of the Laguna Colorada ignimbrite shield. It is the highest mountain in southern Bolivia and towers above the small town of Quetena. Recent INSAR studies have shown that Uturuncu is inflating at a rate of 1 to 2 cm per year over a 70 km area, suggesting that magma is currently intruding into the system. Volcanologists, petrologists, geophysicists, and geomorphologists from institutions around the world are studying Uturuncu to understand the history and current unrest of this beautiful volcano.
Lavas erupted at Uturuncu are dacitic in composition, but also contain andesite inclusions, norite nodules, and crustal xenoliths. Ages from the lava flows and domes range from 890 to 271 ka.
Spectacular views of llamas grazing with Uturuncu looming in the background are common sites in Quetena Valley.
A rough road leading to an abandoned sulfur mine winds up to the saddle between Uturuncu's twin peaks. From this road you can hike up a few hundred feet to the top of Uturuncu and view the APVC from one of the highest points in the region.