The largest volcanic eruption in Iceland since late glacial time originated in the Mýrdalsjökull glacier, during the period of cold climatic conditions of the middle Younger Dryas stadial about 12,000 years ago. Tephra from this eruption is found in several places in northern Iceland usually within sand and gravel. It fell on the glacier which still covered much of the country and was subsequently washed off as the glacier melted, mixing in with glacial deposits. One such place, called Stöplar, is found above Heiðarbót in the Aðaldalur valley. At this location, the Skildingahraun lava which erupted from Reykjaheiði, flowed through the Geldingadalur valley and solidified against the margin of a glacier occupying Aðaldalur and formed a substantial brim. The Vedde-tephra, mixed with sand in different proportions, is found in a sand quarry at Stöplar but is distinguished by its light colour and porous glassy shards. This sand, combined with the pumice, is considered very suitable for cultivation in greenhouses.