- Is there going to be an eruption? Possibly. It is hard to know how serious it could be. At end point it could diminish. So, she is telling me that 'faults' are developing and that fish are dying, that there is a lot of 'earthquake activity. This is of course signs that the volcano is getting more intense. There would appear to be magma flowing into the chamber below the lake.
- What will happen? So I'm telling her I don't know the history of the earthquake, but there are several risks: (i) Pyroclastical surge from the volcanic centre, or less likely a new centre. She is curious - what new centre? Where? (ii) The risk of pyroclastic and aerial ash falls, which is of more concern to her family, as it potentially covers a wider area, and can blast out at oblique angles like Mt St Helens (Washington). Finally, there is (ii) The longer term prospect of flowing of infrastructure by rising land levels. The faulting is relatively minor, though it does obstruct traffic. There is also toxic (i.e. H2S or H2SO4) emissions from the volcano, whether the crater, or belching lake floor. c. The history. So, she goes off and researches, and she sends me all this information about the history of the 1911, 1968 and 1972(?) eruptions. She is describing some interesting facts that attract my interest. That there is a number of craters under the lake water level. She comes back and tells me that there are 'fissures' (faults) opening up in the Lemery, Agoncillo, Talisay and Taal areas. And I know these places, because I have driven with her family all over the area. And I'm thinking, this there could be a pattern to this. She tells me there is earthquakes at 14km in Lemery area, and I'm thinking this could be feeding the main crater, or it could be a 'new volcanic centre' under formation. This would account for the rising or 'inflating' land in this (Lemery) area, that would have the effect of choking off the water flow from Taal Lake to the sea, causing future flooding.
- Will this impact her family? So, she sends me this map. The lines drawn on are mine. d. Regional to tectonic structural interpretation. Now, take a look at this map. Paluan was the scene of an earthquake today at 16km depth. So, I'm wondering if these is any structural control. At the same time, she sent me this diagram below, from the Philippines Volcanic Centre. I went looking at the relationship between this Paluan earthquake and the volcano in Taal. So, when you look at these faults, I'm seeing a clear trend - NNE to SSW.
4. What is the trend? Well, what did you expect? I went looking to Google Maps, and noted 'the lineaments in the Philippines crust with strong SSW-NNE trends, and it was all consistent. It left me wondering whether this was a transform fault, a subduction zone, or a spreading zone. But it was interesting because macro-scale structural trends were apparent, and they extend to Metro Manila. Why is this important? Because the historic record for humans isn't long or reliable. Geological time is 'billions of years'. What if Taal is a super-volcano like the eruption that created Lake Taupo in NZ, then serious risks are possible to a major city. It is early days. Frankly, I don't know much of the geological history of the Philippines. You can see from Google Maps, that this area is on the 'Ring of Fire', on the Western fringe of the Pacific Ocean.
Andrew Sheldon andrewsheldon.info