I read somewhere that it’s not unusual to have increased earthquake activity associated with volcanic eruptions. Does that mean there is a relationship between volcanoes and earthquakes, or could it be just a coincidence? One can imagine that volcanoes might release pressure that might otherwise increase earthquake activity, but that could just be nonsense.
Does volcanic activity increase, decrease or have little effect on the number of earthquakes in a specific area?
Volcanoes and earthquakes certainly do have an association, but not all earthquakes are caused by volcanoes.
If the sub-ground is moving with magma flowing, you can betcher ass there will be earthquakes nearby.
It’s more that some volcanic activity (e.g. US West Coast, Japan) and major earthquake zones are caused by the same thing
But not all volcanoes are strongly associated with quakes. So-called “hot spot” volcanoes (Hawaii, for instance) are different and aren’t necessarily as associated with quakes…
You sometimes hear about “earthquake swarms” that are attributed to magma moving around underground and which can sometimes be a predecessor to a volcanic eruption. For example Yellowstone has them fairly regularly. However, most of the earthquakes associated with these swarms are fairly deep and fairly low magnitude so they’re usually not even noticeable without instruments let alone damaging.
There was a very active volcano in Iceland from August 2014 through a couple weeks ago. Bárðarbunga - Wikipedia
Here’s the Icelandic government’s English-language webpage giving the day-by-day behavior of the volcano in March. Bárðarbunga and Holuhraun - overview | Articles | Icelandic Meteorological office The first couple paragraphs include links to the earlier month’s day-by-day pages.
If you read the volcano’s history starting in August you’ll see it announced itself with massive earthquake swarms, then ground swelling and eventually lava on the surface.
It was pretty exciting to follow day to day when nobody knew what was going to happen but they were concerned it could get really, really big. A huge amount of lava migrated from under the volcano to another area about 20 miles away. A lot of rock got stretched and moved in the process, with a lot of earthquake action.
The wiki article about the eruption at 2014–2015 eruption of Bárðarbunga - Wikipedia is also pretty good.
These volcanoes behave very differently too. The “Ring of Fire” volcanoes on the US West Coast and Japan tend to be very explosive. They sit dormant for long periods of time, but when they decide to go kablooie, they go
K A B L O O I E ! ! ! ! !
and blow up all at once with a mighty explosion.
The Hawaiian-style volcanoes, however, just sit there and chronically burble and fume and splatter and drool magma, like putting candles into a straw-wrapped wine bottle and letting the wax dribble down the sides. They don’t do the big sudden explosions like the others do.