Authorities in Iceland have warned tourists and other spectators to stay away from a newly erupting volcano that is spewing lava and noxious gases from a fissure in the country’s southwest. The eruption began on Monday afternoon in an uninhabited valley near the Litli-Hrútur mountain, some 30 kilometers, or about 19 miles, southwest of the capital of Reykjavik. Aerial footage shows streams of orange molten lava and clouds of gases spewing from a snaking fissure about 900 meters, half a mile, long. The Icelandic Meteorological Office said “gas pollution is high around the eruption and dangerous,” advising travelers not to enter the area. By Tuesday morning, scientists said the fissure and the volume of the eruption had shrunk.