"Where the very air you breathe is a poisonous fume." - Boromir
To the right are numerous vents. Which look to be sizeable. They are dwarfed by the pillar next to them.
The large plume is emerging from the crater, which in turn is situated in the caldera (defined by the cliff borders at the edge of the photo & off-camera somewhere to the left.)
We were told that the caldera itself was filled as a lava lake. That would be a 2 MILE DIAMETER. LAVA. LAKE.
The crater itself is about 1 Km in diameter.
It seemed even larger in person.