Throughout history, there have been many types of human disasters with natural causes: volcanic eruptions, earthquakes, tsunamis, monsoons, hurricanes, tornados, floods, droughts, blizzards, etc. The Peruvian Andes are no exception, being an area prone to earthquakes, El Niño floods, landslides, ice avalanches and glacial lake outburst floods. One of the earliest such disasters occurred in 1725 when an earthquake triggered an ice avalanche from Mt. Huandoy that wiped out the town of Ancash (just north of modern-day Yungay) and its 1500 inhabitants. As for more recent disasters, many people still have personal memories of the devastating 7.9 Richter scale earthquake of 1970, which killed around 70,000 people in the department of Ancash and provoked an ice avalanche from Mt. Huascarán that buried the city of Yungay and its more than 15,000 inhabitants. This was the deadliest seismic event in the Western Hemisphere until the cataclysmic 7.0 Richter scale quake that hit the city of Port-au-Prince, Haiti, on January 12th, 2010, killing about 222,570 people.
In terms of glacial lake outburst floods, the department of Ancash has a tragic history going back to 1941, when Lake Palcacocha broke through its alluvial dike and produced the biggest outburst flood ever to pass through an urban area. There were two lakes called Palcacocha (or Acoshacocha) and Jircacocha (or Cojup). It is believed that the morainal dike of the upper lake (Palcacocha) was weakened when an ice avalanche from the glacier produced a great wave that flowed over the dike made of glacial detritus. Consequently, a great volume of water rushed down the Cojup Valley and burst through the other lake (Jircacocha), releasing a combined flood volume estimated to have been between 8 and 12 million cubic meters of water. Within minutes it reached the city of Huaraz and erased much of the northern expansion district called Centenario.
What was lost? Some accounts place the death toll at 5000 or higher, but this seems somewhat overstated and there are no available records to consult that give a detailed list of names. About 500 cadavers were recovered and buried in mass graves in the Pilatarac cemetery in Huaraz. Fortunately, the flood did not hit any large rural settlements, such as Unchus, before reaching the city, and only affected the sparsely-populated northern sector, not the heart of the city south of Avenida Raimondi. In addition, since it occurred on a Saturday morning, schools were not in session, so many students were saved.
One of the greatest individual losses was a brand-new, two-story Tourist Hotel, built by the national government and just inaugurated five days before the flood. It was torn from its foundations and carried relatively intact for some distance before being smashed into the Santa River to the west. It would never be rebuilt. Other architectural casualties were the School of Arts and Trades, a Boys’ Vocational School, the National Women’s School, the Lawn Tennis Club, the slaughterhouse, various new chalets of wealthy families, and every bridge over the Santa River north of Huaraz, including three near the city of Caraz. Damage to the track of the Chimbote-Huallanca railroad was so extensive that it would eventually cost over 2,000,000 soles to repair. As if to replace this human architecture with natural monuments of its own, the flood left in its wake many gigantic glacial boulders as big as a house and smaller ones covering a wide swath through what had been the newest section of Huaraz. This area of devastation would stay essentially unmodified for the next thirty years.
Before the disaster, there had been some warnings made by Dr. Hans Kinzl, an Austrian glaciologist, based on observations he made in 1939-1940. Some of his photos show Lake Palcacocha dangerously full to the top of its alluvial dike. In later years, there was another outburst flood on the eastern side of the Cordillera Blanca that inundated the town of Chavín de Huántar and buried the famous archaeological site. The safety lesson was finally learned and a program to reduce the volume of water in various glacial lakes was begun in 1951 by the so-called Lake Control Commission of the Cordillera Blanca.
Now, the threat of another outburst flood has returned. The volume of Lake Palcacocha has increased greatly from 5 million cubic meters after the 1941 flood to 17 million cubic meters currently, mainly due to retreat of the glacial tongue, resulting in a lengthening of the lake itself. What can be done to reduce the threat of flooding? One safety measure is to reinforce the artificial dike installed at the lake outlet. It could be strengthened and heightened. Another measure would be to further lower the level of the lake, reducing the volume significantly. So as not to forget the tragedy of 1941, there is still one enormous boulder left from flood on Gamarra Avenue in Huaraz. It serves as a base for a cross that commemorates the people who died in that startling disaster, soon to be recalled on its 70th anniversary, December 13, 2011.
By: Steven Wegner.