Katla is a 1450 m high crater in Mýrdalsjökull Glacier. The crater rooms about all Reykjavik city with around 17 km or 10.5 miles in diameter.
Usually it is covered with ice and it erupts typically every 40 to 80 years with gigantic water flood when the magma and lava melts big number of ice in a very short time. The last big eruption was in 1918 so it is ready to do something.
Geologists expect it to erupt any time from now but with some warnings from tremor and many numbers of big and small earthquakes. Look at the earthquake map (link below) if you are travelling close to Katla. Some small earthquakes strikes the crater each month with non or little damages to the nearby roads and buildings and usually more after the summer when the ice has melt a little and the pressure on the volcano is less.
When everything is quiet with no activity it is nice to go into some ice caves and it is possible to go with some tour guides and tour companies to see this once in a lifetime thing.
