Tornillo Earthquakes - John Seach

Tornillos are long period volcanic earthquakes. Each tornillo lasts for several minutes and the amplitude
decreases producing a screw-like pattern on the seismograph.

Long period seismic events are caused by pressurised fluid movements close to the surface.
Tornillos are an indicator of impending eruption at Galeras, Redoubt and other volcanoes.
The tragedy at Galeras volcano (1993) when 9 people were killed was preceded by tornillo earthquakes.
Tornillo earthquakes were observed before the scientists entered the active crater but were ignored.
 

Tornillo earthquakes
www.volcanolive.com
Copyright John Seach