An eruption started between Sýlingarfell and Hagafell at 10pm. An earthquake swarm started in the magma intrusion north of Grindavík around one hour earlier.There is a risk of lava flowing to Grindavík, says Kristín Jónsdóttir of the Icelandic Met Office.The worst possible location, say Þorvaldur Þó...
You have either plutonic or basaltic volcanoes. This is a quiet plutonic one : it's lava flows without explosions, so, there could be much worse scenarios. But still, it is a big one. Edit : My use of "plutonic" might be outdated or wrong : I think this is the old way it was described, but today, I cannot find a reference to support it.
It's all about how much silica is in the lava - not much and you have basalt, fairly runny so the gas escapes and you get fire fountaining and lava flows. More silica gives you very viscous lava like rhyolite or andesite - traps the gases, far more explosive and dangerous eruption styles.
You are right
...and my use of "plutonic" is either outdated or plainly wrong.
I found this for anyone who wants to read more : https://en.m.wikipedia.org/wiki/Lava
"Properties of lava"
Because of the role of silica in determining viscosity and because many other properties of a lava (such as its temperature) are observed to correlate with silica content, silicate lavas are divided into four chemical types based on silica content: felsic, intermediate, mafic, and ultramafic.
The difference there was that it came up under the glacier Eyjafjallajökull and the magma meeting ice caused steam explosions throwing ash and other material high in the air.