As of early this morning, eruption of ash from the Overlook vent within Halemaumau crater at Kilauea Volcano’s summit has generally increased in intensity. Ash has been rising nearly continuously from the vent and drifting downwind to the southwest. Ashfall and vog (volcanic air pollution) has been reported in Pahala, about 18 miles downwind. NWS radar and pilot reports indicate the top of the ash cloud is as high as 10,000 to 12,000 feet above sea level, but this may be expected to vary depending on the vigor of activity and wind conditions.
Ash emission from the Kilauea summit vent will likely be variable with periods of increased and decreased intensity depending on the occurrence of rockfalls into the vent and other changes within the vent.
At any time, activity may become more explosive, increasing the intensity of ash production and producing ballistic projectiles near the vent.
A Red alert means a major eruption is imminent and all aircraft are to stay the hell away.
These events can throw ash high up into the atmosphere where the jet stream takes them for a ride around the world. The explosions also toss rock around the island at great distances placing the inhabitants at risk of severe injury or death.
And looking at the history (c/o the US Geologic Survey) this volcano seems primed to enter another extended period of explosive eruptions. So, not just one or a few but a long series of them spread out over many years.
And yes, volcanic ash in the jet stream does impact global temperature. It makes the planet cooler.