The 2010 eruption of Iceland's Eyjafjallajökull. Image: NASA Earth Observatory, taken May 10, 2010. I noticed an article over on Discovery News titled "Top 5 Volcano Questions Solved". Now, I don't know if I agree with their choices of the "top 5 volcano questions", but it go me thinking, if these are the "solved" questions, what are the outstanding questions? As with any list like this, the ranking of questions is horribly subjective and considering I'm a petrology and a volcanologist, interested in both the physical event of eruptions and the evolution of magma in the crust, my questions are skewed towards the fundaments of magmas (as opposed to "which volcano erupted when"). If you disagree with my choices, add your thoughts in the comments -- always a lively discussion when we can ponder the multitude of mysteries to solve in volcanology. My Top 5 Volcano questions:1. How is magma stored under a volcano? With all we know about magmatism and volcanism, how exactly magma resides under an active volcano is still a mystery. The problem is that we can't just slice through the top 5-10 kilometers of the crust and see where all the magma is. Even with the best seismic imaging, which uses seismic waves passing through different material to image the state of the crust (i.e., what is solid rock versus what is molten or partially molten), we only get a fuzzy image, like trying to look at someone through muslin. When we can see the plutonic record (that is, magma that cooled underground), what we're seeing is the last gasp of a magmatic system that may (or may not) have fed a volcano. How much of that pile of granite was active and molten at any one time is very difficult to determine ... and was it a lens of 100% melt and then a pile of crystals or was it a network of crystals with melt surrounding it (a "crystal mush")? We can get some sense of the shapes of magma bodies intruding underneath an active volcano by modeling the deformation of the Earth's surface, but even that has a lot of leeway in terms of the magma being a wide, thin intrusion versus a narrow and deep intrusion. This doesn't even touch on the idea of how different magmatic systems might be, as some of the best studied volcanoes seem to have very different magmatic systems -- Kilauea with its long series of lava conduits that feed the rift zones versus the narrow and deep magmatic system underneath Mount St. Helens. This question leads nicely into question 2...
The steaming crater of Sakurajima in Japan, seen on February 15, 2010. How quickly can volcanoes recharge between eruptions and what controls that timescale? Image: NASA Earth Observatory.2. How quickly can a magmatic system reload after an eruption? This gets into the idea of just how is magma emplaced under a volcano -- does it come as a steady stream or does it come in pulses. We already have a sense that it can do both depending on the volcano, but the real question is how long does it take before you get enough eruptible magma (and what does that mean anyway?) Some volcanoes (like Sakurajima) seem to be erupting little bits of magma all the time but other volcanoes wait thousands of years (or more) between large eruptions. This goes with the rule of thumb that the longest the repose time (time between eruptions), the larger the eruption. However, there is increasing evidence that there are a lot of one-two punches out there where two large eruptions occurred in geologically short succession, like the two White River Ash eruptions. They were both estimated as VEI 6 eruptions but only separated by ~750 years and are thought to have been sourced from the same volcano (but this is still controversial). There is also evidence that some of the large ignimbrites erupted from Yellowstone might be a succession of smaller (but still massive) eruptions. All of this comes back to the idea of recharge: just how long does it take to get a volcano ready to erupt again? 3. Are there any truly predictive events prior to an eruption? Here is where the rubber meets the road: can we ever predict a volcanic eruption. By this I mean being able to look at the signs of volcanic unrest like earthquakes and tremor, degassing (carbon dioxide, sulfur dioxide and other volcanic gasses), deformation of the land surface and being able to say "this volcano will erupt in 3 weeks" (and then being right about it). Contrary to what might be out there on the internet, we have no way to do this, rather we can offer probabilities of an eruption (e.g., "likely in weeks to months"), which can be difficult to translate to risk for people living near the volcano. If we can actively monitor volcanoes to look at all the changes at the volcano before an eruption, we might be able to find a parameter (or more likely, a bunch of parameters working in concert) that can give us a better timetable for an eruption. However, this means we need to fund monitoring equipment and people to look at all the data that the equipment generates -- something that is not in vogue in many countries right now. 4. What controls "flare-ups" of magmatic activity?Why is the Kamchatka arc much more active than the Cascades? Why did South America and North America experience a period of massive caldera volcanism 20 million years ago that seems to have petered out today (the so-called "ignimrbite flare-up")? What causes the changes of volcanic output globally over geologic timescales? These questions all boil to looking for the roots of volcanic productivity, which likely lie in plate tectonics. Even though over the Holocene (last 10,000 years) we know that volcanism hasn't really sharply increased or decreased globally, there are definitely periods in the geologic past when volcanic activity was much higher than today.
Ash from the Puyehue-Cordón Caulle eruption spread around the globe, as seen in this June 13, 2011 image of ash from the eruption over Tasmania. Image: NASA Earth Observatory.5. What are the key reasons why some volcanoes strongly effect global climate and some don't?Again, a topic rife with speculation, but it is clear that some very large eruptions have a profound impact on the global climate -- think about Tambora or Krakatoa -- while other massive events don't seem to perturb climate much (see the White River Ash mentioned above). We've also seen that some smaller eruptions have a much more profound effect on the climate than we might have expected. A lot of it might be the location of the volcano and the atmospheric dynamics that spread the ash and volcanic aerosols around the world. Some of it might be the amount of volcanic aerosols released by the volcano, especially the sulfur dioxide. Some of it might be the season in which the eruption occurred and how tall the plume reached. Likely it is a complex combination of all of these factors, but what factors weigh more in the equation and what might be a red herring is unclear. This is why merely noting that an eruption happened to coincide with some climatic shift or extinction isn't enough to make a correlation. Careful examination of the climate record from ice or sediment cores with the volcanic record to look for interrelationships and causal mechanisms might help in starting to parse out what the controls might be, but right now, when a big eruption occurs, we just have to wait and see what the results will be.
