Recent seismic events in the vicinity of the Toba supervolcano have given rise to a great deal of speculation, much of it apocalyptic. Yesterday I watched a magnitude 6.6 quake in progress 30 miles west of the Toba site, and reported that here in an update. There was a previous quake to the south of that on August 31st measuring 5.1.
Looking around the web since then I find many posts claiming that the end is near, it’s going to blow, we are all doomed, the quake was caused by aliens, etc, etc, etc… Unfortunately that’s all pretty standard where volcanoes and earthquakes are involved, but let’s just calm down here a little folks.
While no living person has ever seen a super-eruption (or we would certainly have heard about it) we do have a fair idea what to expect in the way of precursors to such an event, and we are not as yet seeing them with regard to Toba. Those precursors would include swarms of earthquakes in the immediate vicinity of Toba, ground uplift in and around the Toba site, and the temperature of Lake Toba rising steadily. None of this has been seen.
North Sumatra, like the rest of Indonesia, is a seismically active zone, and the recent quakes there are hardly unusual. It’s a subduction zone folks, and that’s just what happens in subduction zones.
Here to the right we see all recorded magnitude 7 and above quakes in the region surrounding Toba since the year 1900. You will note that despite all these over the last century Toba has not erupted, and these are just the big ones. Yesterday’s 6.6 quake would not even show up here.
So will Toba erupt again? Very probably. Will it erupt in our lifetimes? Very probably not. It certainly could, but we currently see no indication that it is getting ready to do so. One or two nearby quakes in a subduction zone do not a super-eruption make.
Probably the earliest indication we could see of something building toward an eruption would be provided by L band INSAR data showing ground deformation around Toba. INSAR, or Interferometric Synthetic Aperture Radar, has been used to map ground uplift and deformation in Yellowstone, and was recently used in Indonesia to monitor Mt. Ibu’s progress toward it’s recent eruption, and we may be quite sure that Toba is being looked at as well. So let’s just chill people.