LAHAR DEPOSITS ON LA LUMBRE RAVINE RELATED TO THE GREAT 1913 PLINIAN ERUPTION OF VOLCAN DE COLIMA MEXICO

At 31 Km North of the city of Colima raises the Colima Volcano, an andesitic stratovolcano with 3860 masl It is considered as the most active volcano of Mexico with more than 25 eruptions in the past 432 years.

Debris flows represent one of the volcanic hazard with more destructive potential because of its movility and capacity of moving blocks of tens of meters of longitude by several kilometers. In the past few years lahars have awakened the interest of the scientific community. Events like those of Nevado del Ruiz and Mount St Helens, represent a good example of the destructive power that these type of granular flows posses and the importance of its study.

The Colima Volcanic Complex (CVC) has a detailed historic record of laharic activity and related phenomena from the XVI century. According with these data this type of activity has claimed more human casualties than any other volcanic hazard in the area.

Within this context, the events ocurred on 1906, 1913 and 1959 are known for its magnitude and the number of victims that they caused. Only the 1906 and 1959 debris flows caused 600 deaths. Nevertheless, the 1913’s debris flows and their related event in the successive years takes special importance because they are directly related to one of the most violent of the XX century in Mexico, the January 20^th pliniana eruption.

So far, there were known locations of some possible lahar deposits that could be related to this plinian eruption. But, there were no solid evidence that can sustain such affirmation, nor there were no specific scientific papers about it. In this work, which was performed on the La Lumbre Ravine, South-West of the crater, we present new geochronological, stratigraphic, sedimentological and textural evidence that prove that these deposits and some others are strongly related with the 1913’s pliniana eruption.

Also are presented new insides related with the flow’s reaching, volume, triggering mechanism and ravine geometry influence in the dynamic and behavior of the flows. New laboratory evidence is presented to explain the few amount of pumice on the deposits and the effect of pumice in reach of the flow. All this information could be used to generate or update hazard maps, taking these lahars as a worst case scenario.