First, it is important to understand that Earth’s climatic and volcanic systems are absolutely linked, in the short term and in the long term. Volcanic eruptions send hot gases and tiny solid particles into the atmosphere (though for all but the biggest eruptions this is short term), they form tall mountains that influence long term wind and precipitation patterns, and some store water in the form of ice and snow. On the other hand, climate, which is the long-term wind, precipitation, and temperature patterns for a given area, determines the air temperature around a volcano, the direction of winds, and how much precipitation falls on the volcano. This affects the hydrothermal systems of the volcano, how far ash will be dispersed on a given day for a specific eruption, the stability of volcanic domes, and how fast the minerals and glass in a volcanic rock will be converted to soil. So, any change to one (climate system, volcanic system), will likely have some impact on the other. No question about that! But, the impact may only be very local and relatively small, or it might be much larger; we can’t always predict ahead of time. We certainly can’t say that rapid melting of glaciers today will cause a flurry of catastrophic volcanic activity! But, just as certainly, we can’t say that global climate change won’t impact specific volcanoes…with potential bad consequences for people and ecosystems around those volcanoes.
While we do not understand many of the details of the links between climate and volcanoes, we know they exist, especially in the long term. But it is complicated! For example, a large volcanic eruption can cause short term cooling of the earth because it can put gases and tiny rock particles into the atmosphere that block solar radiation. But that same eruption also will release greenhouse gases like water and carbon dioxide. So, the same eruption can cause short-term cooling, but contribute to longer term warming. Whether or not the cooling or warming is a bigger impact depending on the specifics of the eruption, and even the atmospheric conditions at the time of the eruption! Below is a list of just a few specific thoughts on ways that volcanoes and climate change will interact.
NOTE: I’ve left out most scientific references here, but will add more detail (with references and figures) in the next few weeks…
- Glacierized volcanoes are likely to be impacted in the most ways. The main impacts of climate change will likely be on glacierized volcanoes (volcanoes that are covered by ice), of which there are between 180 and 450 on Earth right now (see Edwards and Kochtitzky 2015; Waitt et al., 2015; Smellie and Edwards 2016); even though oceanic volcanoes could also be affected if sea levels rise substantially, the impact on any one oceanic volcano will be small as global sea level rise is unlikely to be more than a few ten’s of meters (which is a lot when thinking about flowing of low lying areas!!! But isn’t a very significant pressure change to volcanoes). However, in the Antarctic some volcanoes are covered by more than a kilometer of ice, and locally in Iceland, Chile, Alaska, British Columbia, and possibly Kamchatka volcanoes have ice cover more than 200 m thick (so the pressure change of melting that ice rapidly would be equivalent to rapidly raising sea level by about 180 m, which would require melting quite a bit of the ice on Earth).
- Volcanic systems can be very sensitive to changes in pressure. For example, the 1980 eruption of Mt St Helens was triggered by an earthquake-caused landslide that very quickly released the pressure on a magma that was very near the surface of the volcano. That allowed gas to escape quickly leading to an explosive volcanic eruption. But, different parts of the volcanic system are more sensitive than others. The closer magma is to the surface, the more likely it is to be sensitive to small pressure changes. This is partly because magma, which is melted rock, almost always has some dissolved gases in it (like your favorite carbonated beverage – although with magma the gas is not just carbon dioxide (CO2), but also water, sulfur gases and even fluorine and chlorine). When you open a soda bottle, you release the pressure on the liquid in the bottle, and that allows the dissolved CO2 to form bubbles and escape from the top of the container. In a basic physical sense, the same thing happened to magma when the pressure on it is suddenly released (for example by a landslide – probably glacial melting is unlikely to be fast enough to cause this by itself, but as glaciers melt more rapidly due to global warming, the ice can become more susceptible to sudden, rapid avalanches or collapse if it is on slopes of a steep volcano). Work by several people (including R. Alley and coworkers) on the stability of the West Antarctic Ice Sheet (WAIS) show that it could be much less stable than its eastern Antarctic cousin. Many volcanoes underlie the WAIS, and it is absolutely possible (if not likely, but hard to really estimate concrete probabilities) that rapid thinning of this ice would have some sort of effect on at least a few of these volcanoes.
- Gases drive explosive volcanic eruptions, and the amount of gas in a volcanic system is hard to predict and changes over time. It is hard to predict exactly how sensitive a specific magma system is to small changes of pressure, because the amount of dissolved gas in the magma is difficult to measure. Just as different types of soda have different amounts of carbonation, and until you try the soda it is difficult to know how fizzy it will be. If you have tried the ‘Mentos’ experiments with different types of soda, you probably got very different results. And for a given magma system, gas may be leaking out (like a soda cap that is not screwed on tightly), or gas can even be increasing in the magma if the magma is growing crystals so that the amount of liquid is going down, and that can increase the chance that gas pressure will build. So overtime the chances that a volcano with be sensitive to changes in pressure from melting of overlying ice will change too. Makes predictions pretty difficult…
- Global warming is likely increasing (at least until ice is all melted!) the liquid water at the top of glacierized volcanic systems. Because global warming is causing glaciers to melt more rapidly, it may also be increasing the amount of water in the soil and rocks on glacierized volcanoes. This can affect the volcanoes in at least two ways. First, the water can weaken the underlying volcanic rocks and make them more likely to suddenly breaking and making rock falls and avalanches. This sort of avalanche is one of the most important potential threats from Mt. Rainier for example, and it has probably happened to at least a few volcanoes in Mexico. Also, simply increasing the amount of water in a volcano’s ‘hydrothermal’ system can increase the chances of hot water (phreatic) explosions, and weakens rock deeper within the volcano, making it less stable. Also, because many glaciers move by basal sliding (with the exception of frozen-based glaciers, which are more common in Greenland and Antarctica), increasing the water at the base of the ice may have a direct impact on how fast glaciers move.
- Overlying ice can increase warning time before an eruption. It seems to generally take a few to several hours for a volcano to melt through overlying ice at the start of an eruption, given observations in Iceland from Gjálp (1996) and Grimsvötn (2004, 2011) eruptions. [At its highest efficiency, a cubic meter of lava can melt about 10 cubic meters of ice. But probably for most eruptions the efficiency of melting is a lot less, so it’s probably closer to 1 to 4 volume of lava to volume of ice melted.] However, during this few hours of ice melting, before the eruption breaks through the surface of the ice, it is pretty obvious to people monitoring the volcano that an eruption is in progress. This can provide a few hours during which people can be evacuated, or least prepare. For example, people living in dangerous areas around Öræfajökull or Katla in Iceland could likely drive to safe areas as long as they have even 1-2 hours of warning (assuming they are already prepared to leave).
- Melting of ice due to global warming might lessen the number of lahars in future. On the positive side, melting the ice covering volcanoes means that in the future when those volcanoes erupt they are less likely to have volcanic mudflows (called ‘lahars’) during the eruption! But this loss of ‘potential’ water on the volcano also means a loss of an important water resource for many volcanoes in South America, where glacierized volcanoes are important water storage areas.
- Changes to global high level winds (jet streams) will change ash transport. and precipitation patterns. The global jet streams can change their positions, and they largely control how fast ash and gases from an eruption are distributed. For example, one of the main reasons the 2010 Eyjafjallajökull eruption caused some much problems for air traffic was that the jet stream was in a position to quickly carry ash from Iceland to mainland UK and Europe. An eruption the following year (2011) from Grimsvötn, which actually was larger, bareley made the international news in part because the jet stream carried the ash much further north. If global climate change significantly affects the long term positions of jet streams, it will also directly impact how volcanic ash is distributed globally.
- Changes to global precipitation patterns could affect the stability of volcanic domes and lahar hazards. Studies of lava domes indicate that dome collapses can be triggered by large rain events. If climate change significantly altered patterns of precipitation around volcanoes, it might make some more susceptible to lava dome collapses (increased precipitation) and others less so (decreased precipitation). Also local climate drying could have repercussions for secondary hazards at volcanoes, like dangers from large-scale forest fires (small ones are common in Hawaii when lava moves into forests).