Is there any spectacle more beautiful than eruptions like that in moonlight on a clear night?
What is going on with that ash plume, anyway? It’s not plinian (though Colima is capable of this level of violence). It’s vulcanian. These beautiful close-ups show that a very dynamic environment exists there.
The science of vulcanian ash plumes is very complicated, but as far as you and I are concerned, it involves pressure, heat, and ash (fragmented magma) content. This is way too simplified (please don’t quote me), but as I understand it:
- Pressure. Sudden gas expansion is driving the eruption (perhaps combined with some contact with ground water). This gives Colima’s plume upward momentum thanks to a volcanic jet.
- Heat transfer. Momentum and gas jetting only get the plume so far. That upgoing material is hot, and so there is a point where buoyancy-driven convection takes over.
- Ash content. Differences in the density of small particles can drive movement just as heat transfer does. Simple buoyant convection models don’t take this into account, but you have to for many volcanic eruption plumes. Experts have looked at Colima using thermal infrared equipment. They found, over a five-year period, that Colima’s vulcanian explosions ranged from large events with plumes going as high as 1.6 km (1 mile) to small events producing plumes under 0.6 km (about 0.4 mile). The highest explosion temperatures were associated with dome growth. This very sticky lava tends to plug up the conduit when it forms a dome. Pressure builds up as gases continue to come out of solution in the conduit, and finally the dome explodes. This puts a lot ash into the resulting plume. I think that’s what we’re seeing in the PhotoVolcania video: an explosion, then a dark ash cloud rising above it, then another explosion after a new dome forms, then another ash cloud, and so on. That magma must be really sticky!
Categories: Sunday morning volcano