[Geysers] Blgs Gazette - Geyser, inactive since '98, erupts

[V]

Geyser, inactive since '98, erupts
Variety of changes observed throughout Norris Geyser Basin
By MIKE STARK
Of The Gazette Staff

Lee Whittlesey and Betsy Watry heard it before they saw it. "It 
was like a jet plane," Whittlesey said.

The two were hiking near the edge of Norris Geyser Basin in 
Yellowstone National Park on Saturday, looking for remnants 
of an old hotel.

Around 5 p.m. they heard the roar, turned around and saw Ledge
geyser, the second-largest at Norris and dormant since 1998, 
erupting full-bore, sending a plume of steam about 100 feet 
in the air.


'Now I can check that one off'

"I've been in the park 30 years and this was the first time I'd seen 
Ledge erupt," said Whittlesey, who is Yellowstone's historian. "Now 
I can check that one off."

Watry, who works for the Yellowstone Association, said they were 
shocked at the show that unfolded about a quarter-mile away.

"We just stood there stunned and watched it for a while," she said.

The eruption coincided with other out-of-the-ordinary activity 
at Norris over the weekend, including the eruption of other 
sporadic geysers and changes in the water at the surface.

Henry Heasler, Yellowstone's lead geologist, said the changes 
appear to be part of a "thermal disturbance" at Norris, an infrequent 
and often-sudden shift at the geyser basin that usually comes 
on quickly and then fades away.

There was a similar, though smaller, disturbance in February 
but none in 2005, he said.


Sudden influx

The disturbance, as Heasler describes it, is a sort of "subterranean 
geyser eruption" with a sudden influx of underground thermal fluid 
that briefly affects everything on the surface.

"Imagine if there was a big kind of geyser burp under most of 
Norris," Heasler said.

The latest disturbance was picked up Sunday as visitors and 
staffers noticed changes elsewhere in Norris besides the still-
steaming Ledge. Heasler said the usually quiet Vixen geyser 
has been erupting,

Pearl geyser's water has changed from clear to opalescent, and 
water elsewhere in the basin has turned murky.

And although the geothermal features at Norris became more 
active than usual, Echinus geyser, which is typically somewhat 
predictable, has remained quiet since its last eruption in December.

Duration difficult to predict

The onset of a thermal disturbance is usually easy to see but 
its duration, which can be two days or two weeks, is more
 difficult to predict. Heasler compares the phenomenon to 
the ringing of a bell.

"Some bells quiet down very quickly and others can ring for 
a long time," he said.

Although the cause of the disturbances is still the matter 
of scientific debate, the results have geyser enthusiasts 
buzzing.

Scott Bryan, author of "The Geysers of Yellowstone," said Ledge 
was active in the early 1970s until a thermal disturbance in 
1974. After that, eruptions were less frequent until 1979, 
when it quieted down completely.

The geyser came back to life in 1993 with eruptions roughly 
every nine to 14 days, and fell silent again in 1998.

Ledge is considered the largest geyser in Porcelain Basin at 
Norris, capable of shooting water 125 feet into the air from 
its five vents. Because the geyser is situated on a slope, it 
erupts at an angle and can spray more than 200 feet away.



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