New documentary evidence of the Tungurahua eruption on April 23, 1773, Ecuador

Three documents describing the Tungurahua eruption of April 23, 1773, have been retrieved. The first one is a report of the eruption that has been translated, while the other two are pictographic documents of high quality. Their analysis provides previously unknown information about this eruption. The volcano was not completely inactive since 1645. The eruption started between 4 and 5 p.m. of April 23 in 1773. The maximum activity occurred during the morning of the 24th and the activity continued for more than a month. The Pastaza River was dammed by rocks and sand during 24 h, being over-flooded for almost 5.6 km. At least two lava flows reached lowlands and run into the Pastaza and Chambo Rivers, respectively. The volcanic ash caused important losses in crops and cattle in an area of more than of 3600 km2 located in the western slope of the volcano. Moreover, our primary sources provide evidences that Cerro Hermoso had an important glacier at that time and that the glacier terminus of the Tungurahua was approximately 148 m below the terminus in the early 1980s. This work is an example that an exhaustive analysis of primary documentary sources allows a better characterization of natural hazards that occurred in historical periods.