Santiaguito volcano (Guatemala) is an active subduction zone volcano and part of the Central American Volcanic Arc. It formed in 1922 within the collapse scar of Santa Maria volcano from Santa Maria’s 1902 eruption and is located 11 km south of Quetzaltenango. Santiaguito consists of four volcanic domes aligned from east to west. Present activity is concentrated at El Caliente, the easternmost of the four domes and characterized by small to moderate gas and ash emissions from the central vent and at the eastern flank. We observed substantial dome growth at El Caliente between January 2018 and January 2019. On January 16, 2019, we witnessed an explosion followed by a rockslide at the southern part of the dome leaving a reddish surface visible from INSIVUMEH observatory New OVSAN, 7 km south of El Caliente. This event was accompanied by ash fall at New OVSAN.
In order to gain a better understanding of dome growth, its collapse, and eruption dynamics, we operate a permanent seismic and infrasound network at Santiaguito. Today, it consists of five permanent stations continuously recording at 75 Hz and 100 Hz, respectively. The seismic data is received in real-time via modem from four of the seismic stations. In January 2019, we deployed an additional temporary network consisting of twelve seismometers and six infrasound sensors. We also installed an infrared camera which records images every second and transmits in real-time.
A comparison of seismic and infrasound data with thermal images allows us to distinguish between explosions from the central part of the vent and those from the eastern flank which can also be discriminated by their frequency content. The comparison also reveals that the actual emission of ash and gas persists much longer than the seismic explosion signal which marks only the opening of the vent. Harmonic tremor signals with up to 20 even and odd overtones can occasionally be observed after explosions and coincide with the emission of hot material. The fundamental frequencies of harmonic tremor range between 0.4 and 0.6 Hz and show clear evidence of frequency gliding. The amplitude of the first harmonic has been used to estimate the source depth of the tremor signals. It shows that the source is located at shallow depths less than 1.5 km. The occurrence of harmonic tremor signals on the infrasound data supports this estimate. Volcano-tectonic earthquakes have been registered at depths between 1 – 2 kilometers less than two kilometers south-west of the active vent.