Análisis térmico y evolución morfológica de los Domos Ñuñurco y Cráter Central de la cumbre del volcán Sangay, Morona Santiago, 2003-2019.

Abstract

Sangay is one of the most active volcanoes in Ecuador, whose activity has been observed since 1628. At its summit, extended in an East-West direction, there are five morphological features: Cráter Nor Este, Domos Ñuñurco, Cráter Central, Cráter Occidental and the Domo Occidental. From them, only the Cráter Central (CC) and the Domos Ñuñurco (DÑ1, DÑ2, DÑ3) showed eruptive activity in the last 17 years, having a direct influence over its morphology and therefore the volcanic threat. Based on the analysis of oblique aerial visible and thermal imaging, recorded by the IGEPN between 2003 and 2019, it was identified that the main morphological changes and thermal variations were associated to the Cráter Central and the Domos Ñuñurco. Between 2003 and 2005, the CC was the only which showed activity, characterized for being effusive with the presence of a dome and a lava flow, emitted through the south east. Since 2007, it was observed a changing on the eruptive style, the CC presents explosive activity, the DÑ1 appears over the south east flank and some scarpments are observed within the inner north wall and over the external south wall of the CC, due to the generation of some landslides. Lately, the DÑ1, stopped its activity in 2013 and a new dome is observed at the west of this dome, the DÑ2 in 2012; finally, the DÑ3 appeared in 2014 at the eastern side of the first dome and stopped its activity in 2015. Thus, only the DÑ2, is the one which continue active until those days (September 2021). Additionally, it was possible to estimate that important temperature variations were registered over these morphological features between 2003 and 2019, with minimum and maximum values of 13 to 381 °C for the CC, and of 6 to 370 °C, 29 to 327 °C, and from 6 to 53 °C for the DÑ 1, 2 and 3 respectively. Dimensionally, some changes were registered between 2001 and 2018, having a width range of the CC between 99 and 166 m, meanwhile for the DÑ 1, 2 and 3, it was estimated variations between 21 and 42m, 31 and 54 m and 18 to 36 m respectively. This temporal analysis allows to propose that the Sangay volcano showed four periods of activity between 2003 and those days: P1) March 2003 – November 2005, P2) May 2007 – April 2012, P3) September 2013 – April 2018 y P4) August 2019 – those days; based on four main parameters: a. volcanic activity style, b. thermal anomalies values, c. lava domes appearance, d. scarpments over the CC. Finally, it is proposed that the landslides observed sine 2007 together with the continue activity of the volcano, could have caused a weakness over the southern external wall of the CC, like those generated in the incoming years.