Iceland's tiered system of air travel alerts went to orange last week, then to red with a believed under-ice eruption of the volcano beneath the Dyngjujokull glacier, but has now been eased back to orange. "Observations show that a sub-glacial eruption did not occur yesterday. The intense low-frequency seismic signal observed yesterday has therefore other explanations," the Icelandic Met Office said. The office had therefore decided to move the aviation warning code from red to orange, it said, but since there was no sign the seismic activity was slowing down, an eruption could still not be excluded. The national police commissioner said separately that all restrictions on aviation had been cancelled. Airspace of 140 by 100 nautical miles above the volcano had been closed to aircraft on Saturday.