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Some Katla Volcano Q and A
July 22, 2010
Questions and Answers
I sometimes get some great questions and observations from our readers. Here are a few questions from Fred regarding the Katla volcano, which historically erupts following that of its neighbor, Eyjafjallajokull. I’ve answered them with my own opinion as an observer of the situation.
When Katla follows Eyjafjallajokull, is the time frame based on when Eyjafjallajokull erupts or when the eruption ceases ?
You can look at it either way.
Keep in mind that Katla has erupted many more times than Eyjafjallajokull. Katla has had 38 explosive eruptions as of 30 AD whereas Eyjafjallajokull has had only 4 explosive eruptions in that same time frame.
The interesting thing is that it appears not to be a coincidence that each of the four times that Eyjafjallajokull has erupted, Katla has followed very quickly (relatively speaking). Katla’s average time between eruption is 52 years. Eyjafjallajokull was 692, 209, and 189 years between eruptions.
Other than correlating the known year in which Eyjafjallajokull erupts and then Katla, the only specific month and day dates for Eyjafjallajokull are the following.
Eyjafjallajokull (1821)
START: 19-Dec-1821 STOP: 1-Jan-1823
383 day eruption
Katla (1823)
START: 26-Jun-1823 STOP: 23-Jul-1823
27 day eruption
Katla erupted 554 days (1.5 years) after the 1821 eruption of Eyjafjallajokull. You can also say that Katla erupted only 176 days after Eyjafjallajokull stopped.
We do know that Katla followed Eyjafjallajokull within one year of the other known Eyjafjallajokull eruptions (920 and 1612), but the month and day are not recorded for Eyjafjallajokull.
What is the time-frame relative to a Katla eruption as it pertains to Eyjafjallajokull?
Based on history, the longest time-frame was 1.5 years. So based on the 14-Apr-2010 eruption date of Eyjafjallajokull, that would put the Katla eruption to occur no later than October, 2011. It could also be as soon as tomorrow.
What would be the best indicator on an imminent eruption – if earthquake clusters , how many per min / hour / day ?
I believe that seismic activity and surface deformation are good indicators of an imminent eruption. When magma moves within the crust it usually is noticed by earthquakes or earthquake swarms. Although the presence of signature earthquakes may indicate magma movement, it doesn’t necessarily tell us how much magma is moving. It could be just a little, or it could be a lot. I’ve read articles that support this point of view and there are many factors to consider.
A tip-off would be a rapid change in what was considered normal activity. There is not a strict definition of an earthquake swarm that I know of because they are often different from each other. In the case of Katla over the past several months, based on my own observations I have calculated the average number of earthquakes to be around 2 per day, so we might say that normal activity right now is 2 earthquakes per day.
However, lately there have been as many as 5 to 10 in one day. If this activity were to continue at this pace or to increase in frequency of occurrence, I would venture to say that there is an earthquake swarm going on, many of which have been on the northwest side of the caldera, as of this post. I believe that Eyjafjallajokull was swarming with many more earthquakes leading up to its eruption.
If based on strength of seismic activity , what would be the tipoff ?
Another tip-off could be a larger magnitude earthquake than those that have been regularly occurring, or several of them. That is, above magnitude 3.0 in this case. Several higher magnitude quakes might indicate that something is very imminent.
Katla historically erupts following the eruption of Eyjafjallajokull (which first erupted April 14). Katla is about 10 times more powerful, and has the potential to cause worldwide disruption.
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