I believe the caldera is under the cloud (very likely self generated) to the left of the lava flow, while the snow on the rest of the mountain isn't warm enough to melt (yet). The lava flow probably has melted a few feet of snow, but is primarily losing it's heat to the air.
As to wider impacts, ash clouds affecting airlines is unlikely as it is not under a glacier (which was one of the reasons Ejya's ash went so high - I did hear once that the long version of the name is supposedly locals having a laugh, the volcano is Ejya, the glacier is Ejyafyallajokul, but the news carried on using the long name, so not sure if this is apocryphal), an open caldera would usually preclude a large explosion - unless it cools and plugs the magma chamber, then becomes active again, so it's leaning towards an Etna/Kilauea style effusive eruption.