Evolution of the current eruption in Cotopaxi.

Although a decrease in surface activity was detected at Cotopaxi in the last two weeks characterized by gases and ash less intense emissions, there was an increase in the number of volcano tectonic earthquakes in connection with the internal fracturing of rocks and a tangential deformation rising.

The combination of these factors indicates a possible replenishment of magma reservoir between 3 and 7 km beneath the crater and an increase in internal pressure.

Microscopic examination of the issued ashes shows an evolution of the ash since August 28, with a reduction of the contribution of hydrothermal system and a possible increase in the supply of fresh magma, characterized by free crystals and glassy particles a little bit vesiculated and with a high content of microliths.

Emissions of sulfur dioxide, which is kept around 2,000 tons / day, passed from continuous to pulsatile, with lower values ​​on September 13. According to IGEPN, this corresponds to either a depletion of magma in SO₂, or a decrease in the permeability of the pipe, preventing the evacuation of gas continuously.

An overview of the volcano on September 15 let observed the presence of new fields of fumaroles inside the crater and in the southeast sector, where the temperature reaches up to 43.1 ° C.

The most likely scenarios of evolution
 are :
- More likely an intensification of the eruptive activity in various episodes spread over months, with small pyroclastic flows, as in Tungurahua, with small secondary lahars following the rains or glacial melt,

- A paroxysmal eruption, accompanied by important pyroclastic flows, generating a partial glacial melt, and major lahars.

Sources : IGEPN -Actualización de la Actividad Eruptiva--Volcán Cotopaxi N°16 - 17.09.2015