The Volcano World team ventured once again into the altiplano of South America in October and November of 2010. This time we explored southwestern Bolivia and studied three large ignimbrite systems: Guacha, Laguna Colorada, and Pastos Grandes. Join us on our trip by clicking the links to the right!
Proof that the altitude can do some strange things to your sanity.
The Volcano World team was at it again in 2010. Lead by Dr. Shan de Silva, a new team of graduate students headed out to the Altiplano-Puna Volcanic Complex. This year the focus was on the Pastos Grandes caldera, Laguna Colorada ignimbrite shield, and the Guacha caldera in southwestern Bolivia. The map below shows a general view of the route that we took during the field season that spanned roughly 6 weeks in October and November of 2010. We started in La Paz, the capital of Bolivia and travelled South to Uyuni, on the banks of the Salar de Uyuni. From Uyuni our trip took us to the small towns and villages of Alota, Villa Mar, Quetena, and Huayajara. There were "roads" between many of the towns that accomodate many of the tourists to the region, but many times we found ourselves forging new paths in each of the complexes. Click on the links to the right to see detailed maps of each of the field areas as well as photos of some of the great volcanic features of the area.
The red line is the major route that was taken, though smaller roads are shown in each of the field pages to the right.
We flew into La Paz, the administrative capital of Bolivia, before embarking on our altiplano expedition. La Paz has a population of nearly 900,000 with a metropolitan area of 2.3 million. The city is built in a large canyon sprawls upward onto the altiplano, from 9800 ft near the base to over 13,000 ft in the neighboring city of El Alto. Unlike many cities where wealthier people live at higher elevations, the wealthy districts in La Paz are also the lowest. Affluence decreases up the canyon walls.
La Paz lies on the western edge of the Cordillera Real of the Andes. From the city you can see Illimani, a 21,122 ft peak at the southern end of the cordillera fittingly named the Guardian of La Paz. The city is built on unconsolidated glacial deposits from the past ice age through which Choqueyapa River has cut to form the steep sided canyon. Because of high rainfall, unconsolidated sediment, and steep slopes landslides are a common occurrence in La Paz.
The city embraces its cultural Quechua and Aymara history. We were lucky enough to catch a very colorful parade.
We met our drivers for the trip and stocked up on supplies in La Paz. While we would be able to buy essentials (like toilet paper) in other cities along the way, there are some things (such as peanut butter) that you can only find in La Paz. We also met with Mayel Sunagua at Sergeotecmin, the Bolivian geologic survey, to get permits for transporting our samples back to the states. Finally, we were ready to set off on our altiplano adventure!
Salar de Uyuni is al that remains of ancient lakes of the region. The salt flats cover over 4000 mi2 (25 times the size of the Bonneville Salt Flats of the US!) and contains a large portion of the world's Lithium reserves.
The Bolivian equivilant of the Autobahn. Hmm, needs more salt.
Founded over 100 years ago as a trading post, the town's primary purpose now is to serve the thousands of tourists visiting the world's largest salt flats. The elevation is roughly 3700m and water is scarce so tourism is vital to the town.
Much of our time was spent in the main square, which is filled with shops, restaurants, and hostals, which means lots of tourists.
A relic of one of the many trains that used to support trading in the region. Trains are still a great way to travel here, just make sure to get in line early!
The Pastos Grandes Caldera, measuring roughly 60km N-S and 30km E-W, is the source of 2 known ignimbrite-forming eruptions. The first eruption occured approximatley 5.45 million years ago, erupting the Chuhuilla Ignimbrite. The second eruption occured approximately 2.89 million years ago, erupting the Pastos Grandes Ignimbrite. The ignimbrites account for 1200 km3 and 1500 km3 total volumes respectively. A third ignimbrite, the Alota ignimbite, was erupted from the Cerro Juvina ignimbrite shield to the northeast of the caldera. The goals for this field season were to map the relationship between the ignimbrite and the eastern scarp (outlined in orange) of the caldera (1), determine the relationship between the ignimbrites and Cerro Chuhuilla, a large dome on the northeastern scarp (2), collect samples from the post resurgent domes inside the caldera (3), map the resurgent dome (4), and become familiar with the intracaldera vs outflow facies of the 2 ignimbrites (5). The overall goal of the field work is to map the caldera in detail to identify eruptions of all scales sourced from the complex.
The major features of the Pastos Grandes caldera system are highlighted above. The eastern extent of the caldera is traced in orange and the routes through the area are traced in blue (Pastos Grandes Caldera Loop), yellow (Alota/Villa Mar Road), and red (Cerro Chuhuilla Road). Note that in many cases the roads had to be left behind to forge new paths. for a more Numbers denote the location of the each of the stops.
A view of the outflow facies of the Pastos Grandes Ignimbrite (top) and the Chuhuilla Ignimbrite (bottom) with the Alota Ignimbrite, erupted from nearby Cerro Juvina at 5.23 Ma, in between. This stratigraphic sequence is common on the northeastern flanks of the caldera.
A view northeast from the resurgent dome to the eastern scarp of the caldera. The distance is nearly 17.5km covering the entire width of the eastern moat. Intracaldera Pastos Grandes Ignimbrite covers the base of the scarp in the distance.
The towns of Alota and Villa Mar served as our base camps when looking at outcrops along the collapse scarp. Both towns are quite small, but had more than enough aminities to keep us comfortable. Although, at that point the only thing we needed was a bed!
The streets of Alota had the feel of the set of a western movie.....
and our hostal was a little crowded from time to time.
The first goal of the field season was to determine the relationship between the scarp itself and the Pastos Grandes Ignimbrite. Questions regarding the area revolve around the age of the scarp. Is the scarp a remnant of the Chuhuilla Ignimbrite eruption, or is it the age of Pastos Grandes? In the field, the goal was simply to determine the contact relationship; the exact age of the scarp will be determined by age dating techniques in the lab. An excellent contact relationship, shown below. can be found just west of the town of Villa Mar.
In the Pastos Grandes Ignimbrite, pumice is rare but found to have phenocrysts quartz, plagioclase, biotite, and sanidine (Salisbury et al., 2010). The intracaldera facies commonly contains dense juveniles, and fiamme.
A view West towards the collapse scarp. From this vantage point the scarp lavas can be seen through a small canyon cut in the Pastos Grandes Ignimbrite.
Looking North at the scarp lavas which are covered by the outflow of the Pastos Grandes Ignimbrite. A yellow line highlights the contact.
Looking East from the collapse scarp through a valley cut in the Pastos Grandes Ignimbrite. From here the entire outflow facies is visible (all 100m in this location).
Back at the hostal in Villa Mar with the Pastos Grandes Ignimbrite looming overhead. (Yes that is a plane on top of the ignimbrite)
The second goal was very similar to the first. It is known that Cerro Chuhuilla is of roughly the same age as the Chuhuilla Ignimbrite. However, was all of Cerro Chuhuilla erupted at the same time? Was activity here continuous from the time of the Chuhuilla Ignimbrite to the eruption of the Pastos Grandes Ignimbrite? Again, contact relationships were determined in the field, with precise dating of the lavas to be done back in the lab. Multiple lavas were discovered on Cerro Chuhuilla; it was decided that much more detailed mapping will be needed in future field seasons.
In the Chuhuilla Ignimbrite, the pumice is crystal rich with large purple quartz (>5mm) and smaller (≤5mm) biotite. The pumice also contains dense crystal rich enclaves of euhedral plagioclase, quartz, biotite, and amphibole (Salisbury et al., 2010.)
From the eastern moat of the caldera, Cerro Chuhuilla (right) and Cerro Chulucani (left) can be seen to the North.
From the eastern flanks of Cerro Chuhuilla, the Chuhuilla ignimbrite can be seen sprawling out towards the town of Alota, nearly due East of the dome. Cerro Chuhuilla is not the source of the Chuhuilla Ignimbrite, rather it is part of the collapse scarp of the caldera that may date back to the eruption of the ignimbrite at 5.45Ma.
The third goal of the season was to collect samples of all of the Post-Resurgent Domes for age dating and chemical analysis. Very general mapping was done in the area; however, as with Cerro Chuhuilla, it was discovered that much more detailed mapping will be needed in future field seasons.
A map of the post resurgent lava domes and the resurgent dome structure. Smaller post resurgent domes (PRD) are on the flanks of the resurgent dome structure. The collapse scarp (orange line) can be seen North and East of Laguna Pastos Grandes.
Above and below are views of the lava domes in the middle of the Pastos Grandes caldera, as viewed from the West and northwest respectively. Laguna Pastos Grandes, in the forground of each photo, is a popular tourist attraction in the area.
Cerro Chascon is a part of the Chascon-Runtu Jarita Complex, which is a group of 10 lava domes dated at ~85ka. The northern domes are rhyodacites while to the south domes become more rhyolitic. Plagioclase and hornblende are common to all of the domes, yet sanidine, quartz, and biotite are also seen in the northern domes, while clinopyroxene is only present in the southern domes.
Looking South towards Cerro Chascon, the northernmost dome in a chain of young lava domes in the southwestern portion of the Pastos Grandes caldera.
The fourth goal involved one very long day, and a very long hike, up and around the resurgent dome of the caldera. The idea was to get as familiar as possible with the facies associated with the dome and the structures associated with the collapse.
Above is a map of the resurgent dome, some of the lava domes are visible to the northwest. The red line indicates the placement of the cross sectional view below.
An East-West profile of the resurgent dome. The small flat block in the middle is likely a remnant feature from prior to the collapse of the dome. The small hump the the East is a post-resurgent dome named Sombrieta.
Views of the resurgent dome collapse from the East. On the left, the small flat block (sombriacita) is visible. On the right is a look at the internal structure of the dome. Lava flows that likely post-date collapse can be seen draping the collapse features.
Looking southeast from the resurgent dome to Volcan Uturuncu over 80km away. Uturuncu is an active strato volcano in the back-arc of this region. We met a lot of geologists and geophysicists working on and around Volcan Uturuncu.
While working on the resurgent dome we made it over the 5000m elevation mark! The peak of the resurgent dome is over 5700m (18,700ft) elevation.
The fifth goal of the season was quite simple in comparison to the previous days. The idea was to become more familiar with the intra caldera facies of the Pastos Grandes Ignimbrite, looking for any variation in the unit with proximity to the scarp. The results were quite boring, as the facies seems to be pretty unifom along the inner flanks of the caldera scarp.
The well-indurated intracaldera Pastos Grandes Ignimbrite contains dense juveniles and fiamme (flattened glassy pumice).
Looking West into Chile, across the western moat of the caldera which is completely filled with intracaldera Pastos Grandes ignimbrite.
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.
The 2010 field work done down Bolivia from October 20th to November 16th covered an area of 2948 km2 full of volcanic rocks from Los Lipez at the Altiplano, Southwestern of Boliva. Here 1150 km2 belong to the Guacha caldera and 10 days of this field season were dedicated to know and actually understand this enormous caldera.
Evidence shows the Guacha caldera experienced several episodes of eruption, collapse and resurgence. Some of those features are shown here aimed to solve the history of this volcanic center which geology is beautifully exposed in one of the highest, coldest and driest place in the world.
Stop 1 22°33'47.20"S/ 67°16'48.73"W/4644 m
Domes and intracaldera units
Totoral dome.- Located at the northeast edge of the caldera the Totoral dome is composed of a sequence of pyroclastics flows, blocks and ashes deposits ~100 m thick.
Pict. 3.- Shan walking toward the andesite outcrop located at the northwestern scarp of the caldera
Negreal del Totoral andesite.- A dark greenish isolated outcrop located to the west of the Totoral dome corresponds to one of the more mafic bodies belonging to the Guacha caldera.
Pict 4.- Outcrop of proximal Guacha ignimbrite next to Laguna Busch. It seems that overlies over an older lava or a welded flow unit?
Guacha Ignimbrite.- A proximal ignimbrite close to the Laguna Busch (picts 4) corresponds to the Guacha ignimbrite overlaying a dark grey porphiritic unit (welded?).
Pict 5.- Beautiful Laguna Busch
Pict 6.- Outcrop of younger (?) breacciated intrusives at the eastern scarp
Pict 7.- Brecciated intrusive dark grey dacite ‘bubbles’ surrounded by light dacite ‘bubbles’
Brecciated Intrusives.- Located at the eastern edge of the caldera arquate scarp a semi circular body of ~2 km diameter is made of brecciated intrusive (picts 6 and 7). To the north is bordered by sequences of sandstones, arcoses, conglomerates and travertines (?).
Pict 8.- East view of the moat (summit of intrusive)
Pict 9.- Camp set on the East side of the caldera, the wind direction is inferred by “Paja Brava” plants alignement. On the horizont the Zapaleri volcano as triple point between Argentina, Chile and Bolivia
During that night (and some after) we experienced how cold and severe the winds are on this region, freezing temperatures, several grades below 0˚C, make freeze our own breathe inside the vents! ... anyway the landscapes worth it!!. On picture 9, Jason vent is experiencing the severe wind suggested by the lineated plants (Pajas Bravas). On the background the Zapaleri volcano, which is the triple point were Argentina, Bolivia and Chile met
Stop 2 22°41'05.07"S/ 67°16'23.5"W/4846 m
Pict 10.- Proximal Tara Ignimbrite. A 20 cm thick coarse grain sequence showing cross bedding, clasts supported (almost no fine material). This surge deposit has horizontal continuity and varies upward to a silky flow deposit and a “sillar” or vapor phase
Tara ignimbrite.- Outcrops related to the 3.49 Ma Tara ignimbrite were observed, a proximal one, close to the eastern scarp and a distal one, outside of the caldera edge.
Pict 11.- Distal Tara ignimbrite underneath the Zapaleri volcano
Pict 12.- Distal Tara Ignimbrite over older volcanic basement three surge deposits are seen close to the base
Outside the margins of the caldera a very well exposed sequence of distal Tara ignimbrite was described (actually we were in Argentina here). On top lavas related to the Zapaleri volcano, cover this 60 m thick sequence (pict 11)
Stop 3 22°39'4.39"S/ 67°24'38.07"W/4769m
Guacha Ignimbrite.- The closer outcrop toward the resurgent dome is the Guacha vitrophyde. It outcrops in the ENE side of the caldera, conforming a very conspicuous unit, since is darker than the distal ignimbrites. (pict 13 and 14).
Pict 5.- Dome overlaying the Guacha vitrophyde
Pict 13.- Outcrop of vitrophyde white ignimbrites maybe correspond to Tara ignimbrite ?
Stop 4 22°37'20.90"S/ 67°39'54.10"W/4548m
Pict 14.- Outcrop of Puripicar Chico ignimbrite
Stop 5 22°43'4.74"S/ 67°27'25.51"W/4802m
Resurgent dome.- The “trip” towards the resurgent dome is difficult, since is very remote, very high (~4800 m) and non populated at all, so at least two jeeps are a need to reach its summit. Getting from the northwestern side following just old tracks we reach the point view showed in pict 18. There we can see the intracaldera tuffs pounded in a sequence of at least 150 m. On picture 18 we can see the intracaldera tuffs are slightly dipping towards the NE.
Following our tour we stop closer to the caldera center where a graben-like structure with blocks dipping north and south were recognized. A halo of alteration (?) on the summit of the scarp is also observed in the distance.
Pict 18.- Guacha dome, view from the NW side. Beds of intracaldera tuffs are dipping towards the NE
Pict 19.- Resurgent dome and semi graben (Inside the caldera)
Our journey continued by the beautiful city of Salta, Argentina, where we met Professors Jose E. Viramonte, Marcelo Chino Arnosio, Raul Tato Beccio (from the Univesidad Nacional de Salta) and Shan de Silva (OSU) to take an International Course of Volcanology in the Centrals Andes from the Nov 24th to 30th
Pict 1-4. Plaza 9 de Julio, Catedral Basilica de Salta and Jamie
Pict. 8.- Las Curtimbres Fm. Ring tuff with radial dikes, base surges, phreatomagmatic activity. Interpreted as one of the roots of volcanism seen toward the North
Pict 9.- Radial dikes cutting surge deposits
Pict 10. Julie and the Mexican crew! Behind the fluvial sequences of Las Curtimbres Fm.
Pict 15.- 12.05 Ma Chimpa volcano shield made of an explosive and an efusive events high K, Plg and hb show reaction borders, mixinf AFC, basaltic magma injection
Picts 17.- At the end of the day the godd deserved Salta beer!!SALUD!!
Pict. 11- Golgota reverse faulting asociated with the N-S trend “COLT” thrusting. Cretaceous units overlay older Pumpovuscan basement
12. Perlite mine (wet glass).- Produced as interactions of a magmatic dome with the water table.
Picts 14.- Distal base surge deposits, topographical control, balistic impact
Tuzzgle volcano.- 500 to 50 kyr old made of an explosive and efusive phase. Obsidian flow is shown as the darker unit