In 1984, Lascar awakened to new activity; satellite images noted the presence of hot spots on the volcano. Landsat images taken during this time indicate that a lava lake may have existed in the central crater, generating a plume of volcanic gases and, in September 1986, a vulcanian eruption happened and dropped ash in Salta, Argentina. This eruption was first noticed when ash fell on Salta, and was accompanied by anomalies in the heat emission from the volcano recorded by satellite. The eruption was also observed by geologists in Toconao, where the explosion was violent enough to wake up people who were sleeping. Observers noted the formation of a cauliflower-shaped cloud that eventually developed into a mushroom cloud with a maximum height of above the volcano. The eruption itself lasted only about five minutes and consisted of two pulses. Ash fall in Salta occurred about one hour after the eruption. This eruption was the most significant of the previous two decades, having a VEI of 3. Preceding historical eruptions did not exceed 2.