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Last Updated: Wednesday, 6 October, 2004, 15:56 GMT 16:56 UK
Mount St Helens throws up ash
By Aoife O'Mongáin

Mount St Helens spews out steam and ash on 5 October 2004
Close-by towns got a light dusting of ash
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.

Map of Washington State

It is likely that magma will be pushed out from the vent soon and the CVO says additional, possibly larger steam and ash emissions are likely in the next few days.

But the observatory stresses the cataclysmic event of 1980 in which 57 people died, will not be repeated.

Nonetheless, the volcano's alert level remains at the maximum level of three, which indicates there is a risk to life and property in the area.

Access to areas within about 8km (five miles) of Mount St Helens has been barred since the weekend, and most air traffic has been prohibited below 3,900m and within 8km of the volcano.

Dramatic pictures of the volcano as it spews out ash

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