Lahars, which is a type of debris flow that contains water, tephra, and rock fragments, occurred during the eruption when it rained heavily near the glacier. This was the first observed lahar in Iceland since the 1947 Hekla eruption. During the eruption the precipitation in the area had been low, but during the night on the 19th of May it started to rain. The rain saturated tephra layers on the glaciers and its surroundings which caused the lahar. The lahar went down a similar pathway to the glacial outburst flood and went into the river of Svaðbælisá and other neighboring channels. As the lahar came down to the lowlands near Þorvaldseyri farm, the speed of it slowed down and deposition started. The lahar covered an area of about 0,4 km2 with a 30 cm on average thick deposit, but the deposition was close to 200 cm in some places, and the total volume of sediments from it has been estimated to be about 200.000 m3. The lahar was first observed by Ólafur Eggertsson, a farmer in Þorvaldseyri, around 09:00 am and the flood reached its peak an hour later. The lahar caused some damage to farmland and the hot water line leading from a well in the mountainside down to Þorvaldseyri farm. The damage could have been much more, but the newly built flood walls held and contained the lahar so it did not disperse more widely.