Field Trip to Peru (EARTH 490 course, Spring 2010) | Wat On Earth

Stephen G. Evans, Ph.D. (Professor, Engineering Geology and GeoHazards)

Department of Earth and Environmental Sciences, University of Waterloo

Figure 1. The 2010 EARTH 490 field trip group on the Amazon/Pacific continental divide near Antamina Mine, Ancash, Peru (May 5, 2010)

Introduction

The 2010 EARTH 490 Field Trip went to Peru to examine aspects of the geology, engineering geology, and geomorphology of the Cordillera Blanca, a major mountain chain within the Central Peruvian Andes. The objectives of the field trip were to examine:

The geology of the Cordillera Blanca.
Neotectonics in the Huaraz region, including the Cordillera Blanca Fault.
The engineering geology of glacial lakes formed by recent glacier melting.
Landslide hazards in the Cordillera Blanca, including the devastating 1962 and 1970 Huascaran events.
The geo-archaeology of the Chavin de Huantar World Heritage Site.
Geological engineering aspects of the Antamina Mine, one of the largest copper-zinc mines in the world.

Twelve students (10 undergraduate students, including 3 from Earth and Environmental Sciences, 6 from Geological Engineering, and 1 from Civil Engineering) and 2 graduate students (1 from Civil Engineering and 1 from Mineral Engineering at the University of Toronto, a Waterloo-graduated geological engineer), a teaching assistant (Keith Delaney), and leaders, Dr. Paul Jasinski and Professor Steve Evans (Figure 1) left Toronto on April 26. The field trip ended in Lima on May 8, 13 days later.

The field trip was based in Huaraz, Department of Ancash, which has an altitude of 3052 m a.s.l. We used a 15-passenger Toyota Hiace mini-bus for travel, fitted to the strict safety requirements of the Antamina Mine and driven by Antamina-certified drivers. Most of the field work during the 9 days in Huaraz, including the visit to the Antamina Mine, was carried out at altitudes above 3000 m (9,842 ft) a.s.l. up to a maximum of about 4600 m (15,091 ft) a.s.l.

DAY 1, Monday April 26

The field party left Toronto at 5:10 pm on Air Canada flight AC 80, arriving in Lima around midnight.

DAY 2, Tuesday April 27

The group travelled from the airport just after midnight and checked-in at the Best Western Embajadores Hotel in the Miraflores area of Lima. The day was spent in Lima and included a lunch meeting with John Pottie, P.Eng, Supervisor of Geotechnical Engineering at Antamina

Mine to discuss the Antamina visit. John Pottie is a University of Waterloo Civil Engineering graduate.

The group checked-out of the hotel and transferred to the Cruz del Sur bus station in the late evening, departing for the overnight journey to Huaraz at 10 pm.

DAY 3, Wednesday April 28

The group arrived at Huaraz at 7 am and checked-in to the Hotel La Joya, where the day was spent getting organized. In the evening the group met with Ing. Cesar Portacarrero, Supervisor of Glaciology and Water Resources for National Water Authority.

DAY 4, Thursday April 29

The group went on a field trip to the Rio Santa valley, north of Huaraz and stopped at the site of a debris flow triggered by an outburst from a lake called Laguna 513 on April 11, 2010. Debris flow deposits were examined near Carhuaz.

Afterwards, the group travelled beside the Rio Santa into the Canon del Pato and examined aspects of the geological engineering of intakes to the 240 MW Canon del Pato hydroelectric generating facility and diversion dam (Figure 2). The intakes feed the six turbines deep underground in the Cordillera Blanca in one of Peru’s major hydroelectric projects owned and operated by Egenor, a subsidiary of Duke Energy International.

Figure 2. View of rockslope stabilization, utilizing anchors and rock bolts, above intakes to the Canon delPato hydroelectric plant. Rio Santa is in foreground of view downstream

Figure 3. Tunnel and rock slopes along the Canon del Pato road, south of Huallanca

The group also examined the engineering geology along the road down to Canon del Pato, including roc slopes and tunnels (Figure 3). This route follows an old railway grade constructed in 1928. The group reached Huallanca and returned through the Canon del Pato and from there back to Huaraz.

DAY 5, Friday April 30

Day 5 was spent on a field trip to Huascarán and Yungay, scenes of the 1962 and 1970 debris avalanche disasters, north of Huaraz. The 1962 and 1970 Huascarán mass movements, originated as rock/ice falls from the mountain’s North Peak, which transformed into higher.volume high.velocity mud.rich debris flows by incorporation of snow from the surface of a glacier below Huascarán and the substantial entrainment of morainic and colluvial material from slopes below the glacier terminus. Water for fluidization of the entrained material originated from the melting of incorporated snow and the liberation of soil moisture contained within the entrained material. Eyewitness reports indicate very high mean velocities for the events; 17.35 m/s (1962) and 50.85 m/s (1970). Both mass movements continued downstream in the Rio Santa as debris floods (“aluviones”) that in 1970 reached the Pacific Ocean, a distance of 180 km. In strong contrast to publications in the geosciences literature, the 1961 Peru census data indicates that the death toll of the earthquake-triggered 1970 event is ~6,000 and that total life loss in the two events did not exceed 7,000 people (Figures 4 and 5).

Figure 4. The site of Yungay before (A) and after (B) the May 31, 1970 debris flow in georeferenced aerial photographs. A: the urban area of Yungay is outlined by a white line. (Servicío Aerofotografíco Nacional de Perú photograph; January 9, 1962). B: the urban area of Yungay superimposed on the debris of the Yungay lobe deposited on May 31, 1970. (NASA aerial photograph; July 14, 1970. Cemetery Hill is visible near the lower margin of both photographs (from Evans, S.G. et al. 2009. A re-examination of the mechanism and human impact of catastrophic mass flows originating on Nevado Huascarán, Cordillera Blanca, Peru in 1962 and 1970. Engineering Geology, 108, 96-118)

All field trip members undertook medicals, required by Antamina Mine for the mine visit in the late afternoon and evening at the Clinica San Pablo in Huaraz.

Figure 5. Students gave presentations on 1962 and 1970 Huascaran events at the statue of Christ at the summit of Cemetery Hill, Yungay. About 100 people outran the 1970 debris avalanche and reached the top of Cemetery Hill to survive.

DAY 6, Saturday May 1

Before leaving Huaraz, the group visited the memorial to the December 1941 debris flood (aluvión) disaster in which about 5,000 people died. The disaster resulted from a catastrophic outburst from Lake Palcacocha, a moraine.dammed lake 22 km upstream.

This was followed by a field trip to the east of Huaraz to examine the Cordillera Blanca batholith, Pleistocene moraines dislocated by the Cordillera Blanca Fault, and glacial lakes recently formed by glacial melting. The Cordillera Blanca Fault is an active normal fault that marks the sharp mountain front of the Cordillera Blanca (Figure 6).

Figure 6. Field trip group on Pleistocene moraine to the west of the sharp fault-bounded front of the Cordillera Blanca batholith.

The group also visited the moraine.dammed Laguna Llaca where engineering works were carried out to mitigate outburst hazard by construction of a dam at the outlet of the lake to protect the spillway channel from erosion during a possible overflow (Figure 7).

Figure 7. Laguna Llaca, a moraine-dammed lake formed by glacier retreat in the Cordillera Blanca. Protective works are visible in foreground and were constructed to mitigate outburst hazard by regulating lake level and protecting crest of moraine from erosion during possible overflow.

DAY 7, Sunday May 2

The group visited the Chavin de Huantar archeological site, focusing on its geohazards. From Huaraz, they travelled east and traversed the Cordillera Blanca mountain range to Chavin de Huantar (3140 m a.s.l.), via the 4516 m a.s.l. Kawish Tunnel. Chavin de Huantar (Figure 8) was constructed by the Chavin culture in ~ 900 B.C. According to geo.archaeologists, water supply for the site was facilitated by the presence of a rockslide.dammed lake in valley upstream of the site.

Figure 8. Plaza of Chavin de Huantar archeological site, now a United Nations World Heritage Site.

The site has been subject to debris flows from upstream glacial lakes. The most recent event occurred in January 1945 when an ice avalanche fell into Ayhuinyraju Lake causing an outburst. The debris buried part of the archaeological site and impacted the town of Chavin resulting in 500 deaths.

DAY 8, Monday May 3

The group visited Laguna Paron, near Caraz, with Ing. C. Portacarrero (National Water Authority). This lake is a major water source in the Rio Santa watershed. Extensive civil engineering works were completed in 1985 to control the lake level for hazard reduction purposes and to regulate the outflow of the lake for hydroelectric power generation purposes at Canon del Pato. These works include the excavation of a 3.3 km long tunnel in granodiorite, which the group had the opportunity to examine. The tunnel resulted in a maximum reduction of 41 m in the lake level (Figures 9 and 10).

Figure 9. Student presentation at Laguna Paron with the Toyota Hiace minibus used during trip.

Figure 10. Field trip group at Laguna Paron. The level of the moraine-dammed lake is controlled by a 3.3 km long tunnel through the Cordillera Blanca granodiorite batholith.

DAY 9, Tuesday May 4

Day 9 was the long.anticipated visit to the Antamina Mine (Figure 11). The group departed very early in morning from Huaraz to arrive at the Casablanca control point. This was followed by a 118 km drive up the Antamina access road, a modern two lane paved highway, arriving at the mine at about 10.30 am.

Figure 11. View into the open pit at Antamina Mine. The depth of the mine is in excess of 500 m.

Antamina is a joint venture between BHP Billiton Ltd. (33.75%), Xstrata (33.75%), Teck Cominco Ltd. (22.5%) and Mitsubishi Corp. (10%). In 2009 the mine produced 343,179 tonnes of copper and 495,420 tonnes of zinc. Operations began in 2001 and the life of the mine will extend to at least 2029. Primary processing is carried out in a conventional grinding and flotation mill at the mine site and the copper and zinc concentrate is transported in slurry form (42% water) through an earthquake-resistant 302 km-long 23 cm-diameter pipeline to the port of Huarmey on Peru’s coast.

Antamina is a polymetallic skarn ore body hosted by Mesozoic carbonates within the Marañon fold-thrust belt. Deformation of the carbonates occurred during the Eocene. The timing of the intrusion is coeval with that of the Cordillera Blanca batholith in the Miocene. Over 90% of the skarn is mineralised with average grades of 1.24% (Cu) and 1.03% (Zn).

The giant 135 m high tailings dam (Figure 12) is the highest in the world and is also the highest concrete-faced rockfill dam on Earth. The design of the dam had to take into consideration the high seismicity of the region and was carried out by Golder Associates. Karst openings in the limestone foundation had to be grouted.

Figure 12. Overview of tailings dam at Antamina Mine. The structure, founded partly on karstic limestone, is the highest concrete1faced rockfill dam in the world and was designed by Golder Associates.

High open-pit mine production yields enormous quantities of waste rock at Antamina which are dumped in massive waste rock piles (Figure 13).

Figure 13. View of waste rock dumps at Antamina Mine. Dump slopes are formed by end-tipping of waste rock from 218 tonne (153m³) capacity Caterpillar 793C dump trucks visible at mid-right.

DAY 10, Wednesday, May 5

Day 10 started with a transect along the Antamina Mine access road. Landslide investigation sites were visited with Antamina and Golder Associates personnel. Throughout the day the group had lengthy discussions on landslide hazard and risk along the 118 km access road, a key element of the mining company Antamina’s risk management strategy. The road is the lifeline to the mine with dense traffic carrying fuel, food, and spare parts to the mine as well as the frequent bus transport of personnel to and from the mine site (Figure 14). The group also visited the famous dinosaur footprints exposed in a rock cut along the road (Figure 15).

Figure 14. Student writing notes on landslide hazard and risk on Antamina Mine access road. Note fuel anker in background illustrating the strategic importance of highway lifeline to Antamina Mine.

Figure 15. Dinosaur footprints exposed in Cretaceous rocks in a road cut, Antamina access Road.

DAY 11, Thursday May 6

On day 11, the group checked out of the La Joya Hotel and mostly spent a free day in Huaraz, but also included a meeting with Ing. C. Portacarrero at the National Water Authority offices. The group boarded the Cruz del Sur bus from Huaraz at 10:00 pm and travelled to Lima.

DAY 12, Friday May 7

Arriving in Lima at 6 am, the group checked into the Best Western Embajadores Hotel in the Miraflores area. The group enjoyed a lunch meeting with John Pottie, P.Eng., Supervisor of Geotechnical Engineering at Antamina to review the Antamina Mine visit. The group travelled to the airport in the late evening.

DAY 13, Saturday May 8

The group boarded for the long flight home to Canada.

Concluding comments and acknowledgements

The 2010 EARTH 490 field trip to Peru afforded a unique opportunity to students to see first hand, active tectonics, glacial geomorphology, glacial and landslide hazards as well as geological engineering aspects of hazard mitigation, hydropower development and massive open pit mining at high altitude in a spectacular mountain environment. The Antamina mine is a state-of-the-art mining operation and our group was very impressed by the way in which the company is addressing challenging technical and environmental issues.

The EARTH 490 class and instructors are grateful to John Pottie, P.Eng. and David Gilbert, P.Eng. of Antamina for their fantastic technical support and for facilitating a memorable visit to the Antamina mine. The group is also indebted to Ing. Cesar Portocarrero (National Water Authority) for leading a spectacular visit to Laguna Paron and the drainage tunnel constructed in 1985.

Finally, all those involved in the 2010 EARTH 490 field trip to Peru would like to gratefully acknowledge the financial support of the J.P. Bickell Foundation, the Prospector's & Developer's Association of Canada, the Dean of Engineering, the Dean of Science, the Department of Earth and Environmental Sciences and the Department of Civil Engineering at the University of Waterloo. Without this support this field trip to Peru would not have been possible.