Múlakvísl a glacier river coming out from under Kötlujökull the southeast glacier tongue from Mýrdalsjökull which sits on top of the caldera Katla. one of the largest and active central volcano in iceland. Katla is the central volcano for the volcano system known as Mýrdalsjökull. In 2010 there was a large eruption in its neighbour Eyjafjallajökull, that many know as the unpronounceable eruption that halted airtraffic for a long period due to an enourmous ashcloud.
A year later in early July of 2011 a large run off from a sub glacial eruption happened in Múlakvísl. (a flood) however no warning signs or any signs of that matter indicated that an eruption had taken place. but where did all the water come from that was so strong it sweept away a big concrete bridge in one piece?.
I recommend that you look at the information signs, that are found here. about this event and it´s aftermath and the increadible reaction taken to cope with the ringroad being cut off. The only roead leading through the area to conect the easter parts of Iceland to the southwest parts.