On 26 February, Iceland's most famous volcano, Mt. Hekla, began erupting at 1819 GMT. The seismic networks of the Science Institute, University of Iceland and the Iceland Meteorological Office recorded a short-term precursory earthquake activity. A seismograph near the summit of Hekla beginning at 1700 detected small earthquakes. The National Civil Defense of Iceland issued a warning, and the public was alerted. Thunder, lightening, and earth tremors accompanied the eruption. A 6-7 km long fissure appeared and a steam column rose nearly 15 km (45,000 feet) into the sky. A discontinuous curtain of fire emanated from the entire fissure. The lava flows down the slopes of Hekla and covers a large part of the Hekla ridge. One lava stream flowed from the eruptive fissure towards the north. A more active lava stream emanates from three craters near the southern end of the eruptive fissure. On February 27, this lava stream was several kilometers long and was advancing at a rate of about a meter per minute. The Coast Guard reported that the new lava covers a stretch of about 3-4 km at its longest. The maximum thickness of the ash sector, 21 km north of the volcano, was 4-5 cm when measured 7 hours after the onset of the eruption. Most of the ash fell in uninhabited areas in the interior of Iceland. The eruption reached its peak intensity in the first hour of the activity. Presently, the lava flows and ash fall pose little danger to human settlement. Geologists said the activity could continue for about a month. Icelanders in the Middle Ages called the volcano the "Gateway to Hell."