Field Guide Stops 31-35


The final section of our trip took us into the Valley of the Spires, to the obsidian ring dike Jarellon, and to the most active volcano of the whole trip, Lascar!

Stops 31-36

Stop 31: Valley of the Spires

Valley of the Spires

23° 3'20.22"S,    67°28'43.26"W
Elevation: 4455m (14618 ft)



Just past the hairpin turn where we first encountered the Filo del Gado, we turned off of the 27 to the dirt road heading East/Northeast into the Valley of the Spires.       

Casey looks at the spires

Here, the winds blow hard and consistently in the same direction.  Millions of years of erosion have worn away the Tara (?) Ignimbrite that once filled this valley leaving only these giant columns.  


Giant stone columns in the Valley of the Spires 

 From there we we headed north on the road to Salar de Tara. 

On the way, we stopped at the famous WMF outcrop.






 WMF Outcrop  





Additional Information:




  • Lindsay, JM, et al.   2001.   La Pacana caldera, N. Chile: a re-evaluation of the stratigraphy and volcanology of one of the world's largest resurgent calderas.  Journal of Volcanology and Geothermal Research, Vol. 106, Issues 1-2, 1 April 2001, Pages 145-173















Stop 32: Salar de Tara


22°57'57.66"S, 67°18'58.32"W
Elevation 4322m (14195 ft)


The Salar de Tara is a beautiful place to camp with spectacular views of flamingos on the lake and the Tara ignimbrite in the distance. While you will be tempted to set up tents under shelter in the little cabins by the lake, beware because they are infested with rats! Camping outside may be the better option.

 Salar de Tara

The Tara ignimbrite consists of two major units: lower Tara and Tara. The lower Tara is known as the Guacha because its source area is the Guacha caldera. It was originally mapped as the Atana ignimbrite but was re-labeled as a Guacha-sourced ignimbrite that ponded in the La Pacana caldera. The Tara lies above the Guacha and is comprised of 4 sub-units labeled 2-5, 5 being the youngest. The Tara is one cooling unit with huge breaks in time.


The Guacha, 5.6 Ma is a crystal-rich, lithic-rich andesite that contains large pumice clasts and bimodal quartz phenocrysts. The Tara, 3.68 Ma contains less pumice and lithics and has a more ashy matrix. Between the Guacha and the Tara is a Plinian deposit that is very crystal-rich and clast supported. 


We had some visitors in our camp the next morning!!!


Did we mention the flamingos...?!


Stop 33: Guacha / Tara / Atana Ig's



22°57'51.84"S, 67°19'37.08"W




This location shows a wonderful section of the Filo Delgado overlying the Tara ignimbrite. The Filo Delgado Ignimbrite is the youngest unit and contains those distinguishable fiamme of obsidian. The middle unit is the Filo Delgado fall deposit that contains banded rhyolites, obsidian clasts and is dominated by lithics. The oldest deposit, underlying the Filo Delgado is the Tara ignimbrite that has an ashy matrix, lithics, and no obsidian and/or rhyolite. 

It was questionable whether the fall deposit should be associated with the overlying Filo Deglado or with the underlying Tara ignimbrite. Because the plinian contains obsidian and rhyolite, it has been suggested to be part of the Filo Delgado deposit. 






22°54'9.12"S, 67°18'52.26"W

This is a great location for seeing the Guacha of the Lower Tara ignimbrite, also known as “Big Yellow” because of its yellow color. The Lower Tara fills in the depressions in the area and outcrops horizontally as a flat plane. In this location units 4 & 5 of the Tara lie directly above the Guacha.


22°52'41.76"S, 67°18'25.68"W

After driving around the area searching for the Plinian deposit of the Tara, we finally found a great exposure of the airfall at this location! The Tara Plinian fall deposit contains abundant pumices with quartz, plagioclase, biotite and magnetite crystals. While the crystals may not appear immediately apparent, with a closer look they are actually found in clusters and are quite coarse. The pumice shows variations in vesicularity, some appear silky and others more gas rich.

Stop 34: Co-Ignimbrite Ash

Co-ignimbrite ash

S22 52 13.71, W67 20 10.78

A co-ignimbrite ash is a cloud of fine ash particles that overrides a pyroclastic density current.The process responsible for the formation of these clouds is call elutriation. The co-ignimbrite deposit overlies the Tara ignimbrite and is capped with dilute flow, surge, and possibly flow deposits. This is the only co-ignimbrite ash deposit ever identified in the central Andes.

co-ignimbrite ash

Image of the co-ignimbrite ash deposit with Bob for scale.

Close up image of the co-ignimbrite ash deposit with hot sauce for scale.

See Sparks and Walker (1977) for more details


Stop 35: Jarellon



22°52.766'S, 67°27.130'W


One of the final stops on our Chilean voyage was Jarellon. Located on the Chile/Boliva border near the La Pacana Caldera, Jarellon is the surface expression of a large ring dike, estimated at less than 5.6 million years old. Notable about the ring dike is the extremely abundant obsidian clasts that are weathering out. Red, black, and snowflake obsidian can be found, much to our delight.  




Note: while breaking open obsidian can be fun, we would recommend wearing gloves and glasses as the shards can be very very sharp.

Stop 36: Lascar



  23°22'15.92"S,    67°44'35.00"W
Elevation: 5488m (18062 ft)

 Panorama of Lascar

Panorama from the Lascar Southern pyroclastic flow

Lascar is the most active volcano in the central Andes.  It is an andesitic to dacitic stratovolcano with six overlapping craters, trending roughly northeast, with the active, fuming crater located near the center.   The largest historical eruption of Lascar took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit.  Grey pumice deposits from the 1993 eruption are visible in the photo above and below.

Pumice flows on the North side of Lascar


 Banded pumice




Light, dark, and banded pumice are mixed in this flow.




And we made a few friends!