The Aleutian Islands region is criss-crossed with corridors for aircraft flying back and forth from Asia to North America (and beyond), so such an impressive ash plume, combined with less then stellar visibility, means that airplanes have been instructed to avoid the area around Pavlof. Remember, large jet aircraft and ash don't mix! The Alaska Volcano Observatory is reporting that seismic tremor at Pavlof is still high, meaning magma is still moving into the volcano and the eruption is going strong (without ground-based visual confirmation.) Luckily for people on the ground, the ash is being blown out to sea rather than towards populated areas like Cold Bay.