Reading an article about Pahoa, I read that erupting Hawaiian volcanoes produce a combination of lava and haze - resulting in clouds that contain hydrochloric acid. Are these as dangerous as volcanic ash clouds? What are the possible consequences for nearby flights?
Laze is produced by lava running into the ocean, which limits both volume and dispersion of harmful products. Volcanic ash can be blown high into the air in astonishing amounts by explosions at a volcano summit, making it possible for wind to spread the particles over a wide area.
The 2010 eruptions in Iceland blew ash several kilometers into the atmosphere and across much of Northern Europe, shutting down air traffic for days. Both types of emissions have abrasive particulates and corrosive chemicals, so the biggest determinants of harm are dispersion and volume. Ash is by far the more dangerous.
see Kileua sends ash 30,000 feet high and this isn't even considered a very explosive volcano.