"The 1961 eruption was preceded by the formation of big solfataras on a N-S line along the eastern caldera wall. The eruption started in the same area two weeks later, on October 26, when an E-W-running fissure, 0.7 km long, opened up. The eruption was of the Hawaiian type, and lava fountains rose to a height of 500 m. Within the first 10 hours or so the lava flow reached a length of 7.5 km and an area of nearly 6 km 2 . When the eruption ended five weeks later the area was 11 km 2 . Until November 5 the lava solidified mainly as apalhraun (aa) lava, but from then on it was more fluid and solidified as helluhraun (pahoehoe) lava. The two lava types differ with regard to their mineralogy. The lava produced before November 5 is characterized by relatively few phenocrysts of plagioclase and pyroxene in a groundmass of black glass that is opaque due to precipitation of ore. Olivine is not found. The fluid lava of the second phase contains more phenocrysts. Olivine is present and the glass brown and translucent. Three new analyses od Askja lavas are presented."