Glance at the news lately and you might see these headlines that would make Kent "ACTION NEWS" Brockman proud:
A snapshot at Google News from the weekend. Let's set something straight. No, we're not around the corner from a VOLCANIC APOCALYPSE. A volcano can show many signs that an eruption might be brewing. These include, but aren't limited to:
Inflation - As magma rises, it takes up space, so the volcano inflates. Sometimes that inflation is subtle, on the order of a few millimeters. Sometimes it is dramatic like the bulge on Mount St. Helens prior to the 1980 eruption (see below).
The bulge on Mount St. Helens (foreground, cracked ground) before the 1980 eruption. The land rose more than 100 meters prior to the blast. USGS.
Earthquakes - I've discussed this before. As magma moves, it can cause earthquakes as it makes space for itself and shattered rock or as it grinds against the sides of the conduit in the volcano. These events generate earthquake swarms (an increase in the number of earthquakes at a volcano) or tremors. Additionally, if there are enough seismometers around a volcano, then geologists can determine where and at what depth the earthquake happened. Taking that geographic information and combining it with information about whether earthquakes are becoming more frequent or stronger, or both, volcanologists can get a sense of whether the volcano is headed for an eruption.
Gas emissions - As magma rises, it loses gases that were dissolved in it. The most common is water, but there is also a lot (as in tons per day) of carbon dioxide, sulfur dioxide, chlorine and more. If you measure the concentration of these gases in the steam plumes from volcano, volcanologists can determine whether magma is getting closer to the surface.
Now, this is great, right? We have "warning signs" before an eruption ... except for two important things that aren't usually discussed:
When? Volcanologists can offer a probability of an eruption, usually qualitatively such as "likely" within some time period (usually nothing longer than a week or two). However, pinpointing exactly when an eruption will happen, especially far in advance, is not possible. So, saying a volcano is "ready to erupt" could mean the next hour or the next year. The changing warning signs can help narrow it down, but as we've seen at Agung, volcanoes don't care for your prognostication.
How big? Volcanoes might show all the warning signs, but trying to deduce how big and what type the eruption will be is challenging. Typically, we fall back on looking at what the volcano has done in the past, but the geologic record is incomplete and larger eruptions are often overrepresented relative to the smaller eruptions that happen more frequently. So, yeah, the volcano might be "ready to erupt" but that eruption might be small (so we don't need to panic).
If we look at the two volcanoes in question from the recent news, we can see how much hype there is versus actual volcanology. In Iceland, there was a brief earthquake swarm near Bárðarbunga, some of which were larger earthquakes over the M4 rating. Now, this volcano just had a year long eruption in 2014 (see below) on its flanks at Holuhraun that was one of the biggest effusive (lava flow) eruptions in the past few centuries. It did not, however, cause "travel chaos" -- that was Eyjafjallajökull in 2010 and to a lesser degree, Grímsvötn in 2011. They produced explosive eruptions that sent ash and debris high into the atmosphere. If Bárðarbunga were to have another eruption like Holuhraun, we should expect lava flows. If it follows the less-likely path of an explosive eruption like it experienced in 1477, then we might see more travel problems. In either case, the earthquake swarm does not mean the volcano will erupt at any minute. Swarms are common at many volcanoes -- and oftentimes they are related to hot water moving the volcano or faults.
The 2014 Holuhraun eruption near Barðarbunga in Iceland. Wikimedia Commons. The same can be said about Teide on Tenerife. An earthquake swarm occurred on the island -- one of the first in decades -- and it lead to speculation that we might be headed to the first eruption in the Canary Islands since 1909. However, that eruption might not occur for years and these earthquakes are likely not even precursors of the next eruption. So, all the media shouting that an eruption might happen "at any moment" are pure fear-mongering over an event that is common at most volcanoes. INVOLCAN, the group that monitors volcanoes in the Canary Islands, hasn't changed the status from "green", its lowest level, due to the earthquakes. So, always take any media source shouting that a volcano is READY TO ERUPT and that the eruption is cause for TRAVEL CHAOS or will DESTROY CIVILIZATION with a grain of salt the size of a Buick. Volcanoes can often show signs of eruption, but the likelihood is that the eruption, if it happens, will be smaller than the media hypes it to be.
