Preliminary map of volcanic potential threat Nevado del Tolima, Colombia, S.A.
DOI:
https://doi.org/10.32685/0120-1425/bolgeol29.3.1988.242Keywords:
Colombia, andesitic stratum-volcano, pyroclasts, lahars, ash flow, hot springs
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Copyright (c) 1988 Servicio Geológico Colombiano
This work is licensed under a Creative Commons Attribution 4.0 International License.
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Abstract
The Nevado del Tolima is an active andesitic stratovolcano located in the Los Nevados National Natural Park, Central Cordillera of Colombia, at coordinates 4.65°N and 75.37°W of the Greenwich Meridian. The volcanic edifice is 1.2 km high, has a slope of 38%, is crowned by an ice cap with a minimum volume of 0.095 km 3 of ice, and reaches a maximum altitude of 5200 m asl.
During its most recent activity, the Nevado del Tolima has produced pyroclasts, which are distributed by fall and flow mechanisms, lahars, and lavas. The eventual emission of these products in the future is a potential threat to the life and property of the people living in the areas of influence identified in this work.
The identification of areas threatened by pyroclast fall was made based on the study of the three major plinian levels produced in the last 14 000 years through the elaboration of isopach and isopleth maps. As1, the area threatened by ballistic projectiles was determined: circle of 8 km maximum radius around the crater; the volume of each emission: between 76.3 and 940.0 million m3; the magma flow rate: from 40 to 75 million kg/s; the height of the eruption column: 10 to 18 km height above the crater: 10 to 18 km high above the crater; duration of each event: 0.26 to 1.74 hours; wind direction that transported the pyroclasts: between N9° E and S71° W, counterclockwise; and VEI: between 3 and 4.
The zones threatened by eventual flows of ash, pumice, slag, and by the collapse of lavas and domes were discriminated considering the dispersion of the products emitted in the most recent history of the volcano and the presence of topographic barriers that would totally or partially impede the passage of these products.
The zones threatened by future lava emissions were identified based on the distribution of those emitted in the past, the current topography, and the expected thicknesses of the flows.
The Combeima, Toche (Coello), Totare, and San Rumualdo rivers, a tributary of La China, which are part of the Magdalena River basin, originate in the glaciers of the Nevado del Tolima. The valleys of these fluvial currents would be the potential channels that could be used for eventual lahars. According to the current topography, the amount of ice available in the ice cap and the lahars produced previously in the Nevado del Tolima, the threatened areas, and the transit time of the lahars to the most populated sites were determined. According to the above, one of the areas most threatened by this phenomenon is along the Combeima River. The banks are inhabited by more than 50,000 people, concentrated especially in the city of Ibagué, where the lahars would arrive in less than an hour.
The future scenario of an eventual eruption of the Nevado del Tolima would consist of an explosive event that would produce an eruption column whose products would be distributed ballistically and aeolian; this column could partially collapse to produce small ash flows. The fall and flow of ash on the ice cap ice would produce the partial melting of the east and induce the formation of lahars that would affect, in its distal part, mainly the valleys of the Combeima, Totare, and San Rumualdo (La China) rivers.
To obtain the final version of the preliminary map of potential volcanic hazard of Nevado del Tolima, with scale of 1:100 000, the number and type of events that have occurred in the last 14 000 years of volcanic activity, the recurrence periods, the threatened areas, and the severity of each type of event are considered. This version is a simple map, a product of translation of scientific information into a simple vocabulary, in which areas of high, medium, and low threat are indicated, without indicating the specific type of threatening volcanic event.
The appropriate use of this map should contribute to minimizing the damage caused by an eventual eruption of the Nevado del Tolima, both in terms of the lives and property of the potentially threatened community. This way it contributes to a better quality of life for an important sector of the Colombian population.
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