The Mount St Helens volcano in the US state of Washington has erupted its largest steam and ash cloud since its resurgence in activity last month.
The cloud reached 3,600m (12,000ft) into the sky and drifted in a northeast direction, dusting nearby towns with ash.
Scientists said steam clouds billowed from the volcano's crater for about an hour on Tuesday morning, local time.
Previous eruptions over the last few days had thrown up much less ash, the Cascades Volcano Observatory reported.
Tuesday's event was the first time the ash content was picked up by the US National Weather Service.
Dr Justin Denny, Health Officer at Clark County, Washington, just west of where Mount St. Helens is located, advised local residents the ash was unlikely to have anything more than an irritating effect on most healthy people.
However, he warned that if there were further, larger eruptions of ash, people with lung problems such as asthma should "stay clear of the ash" by staying indoors and wearing a mask.
He said the ash was mostly made up of dust which causes the irritating effect but it also contains 4% silica. He assured people that there no known long-term effects associated with this level of silica exposure.
Tuesday's emission came from the same vent as those over the last few days but there was additional activity from a new vent nearby in the now intensely deforming dome.
The rate of seismicity was high before the new event but reduced during the eruption and overnight has remained at a low level.
The CVO reports that a bubbling lake has formed near the vents where the ash and steam has been coming out.
Visual observations show the 300m- (1,000ft) high lava dome within the crater has lifted by about 45m (150ft) and it is continuing to rise. Scientists believe magma is now at a very shallow level and hot cracks in the dome are opening which is causing rockfalls on to the south crater floor.