In the past week, the toe of a landslide in Spanish Fork Canyon a mile below the infamous 1983 Thistle slide has moved 16 feet - a bad omen of slides and debris flows that are likely to hit throughout Utah this spring.

In addition, weather watchers are nervous about the possibility of flooding.The snowpack is so great in the Virgin River drainage that "we could have a problem or two on the Santa Clara (river), I suspect, if we had some warm rains when the snowpack was trying to melt," said William J. Alder, meteorologist in charge of the National Weather Service's Salt Lake forecast center.

"The concerns are heightened some in Davis and Weber counties just because of the snowpack that lurks up in them thar' mountains," Alder added. The Great Salt Lake has risen a couple of feet, but not enough to worry about yet.

Landslides and debris flows, the risk of which is intensified by the same heavy snowpacks, remain the more probable weather danger this year.

The slide below Thistle is called the Shurtz Lake landslide. It started creeping last year on top of two prehistoric slides.

What's even more significant than the Shurtz Lake slide itself is that now the ancient slides also have slipped 3 feet, said M. Lee Allison, director of the Utah Geological Survey and the state geologist.

"We've seen an acceleration of movement, and we've seen the underlying slide move," he said. The Shurtz Lake slide contains about 4 million cubic yards of earth while the old prehistoric slide has another 4 million cubic yards.

"We have notified the county and state emergency officials that there is accelerating movement and the potential for this landslide material, per chance, to move into the river channel." If it does get into the Spanish Fork River the slide probably won't block the river because there's no mountain on the other side to buttress it.

The movement was reported to Allison by a class from Utah Valley State College, Orem, which has been monitoring the Shurtz Lake slide region by driving stakes and measuring their displacement.

The Thistle landslide caused an estimated $225 million in damage, drowning the tiny town of Thistle under 150 feet of water, covering the Denver & Rio Grande Western railroad tracks and disrupting traffic for months while road crews cut a new path for the buried stretch of U.S. 89. But experts doubt a new landslide in Spanish Fork Canyon would be that destructive.

Davis County officials are preparing for a wet and wild spring.

On Monday, the Davis County Com-mission assumed the flood- control responsibility for three more stream channels within Clinton, West Point and Syracuse. The county now controls 27 channels, said Sid Smith, Davis County Public Works director.

"We are watching the streams very carefully," Smith said.

Of the greatest concern are the snowpacks in the southern part of the county. In some of the lower elevations above Bountiful the snowpack is more than 200 percent of normal and above Farmington, approximately 160 percent above normal.

Despite the high levels of snowpack, Smith isn't ready to panic.

"We've got a couple of weeks before we start getting nervous," he said.

Instead, residents have begun the annual battle to prepare for the possibility of a high runoff. Many cities, such as Centerville, will include channel clearing as part of a citywide cleanup day later this month.

Flood-control measures have also begun in Weber County where reservoirs are being lowered and rivers are running high, said Ivan Flint, director of the Weber Basin Conservancy District.

"We're trying to prepare for a heavy runoff," Flint said.

He said most of the reservoirs are at 40-50 percent of capacity, which will buffer much of the runoff. But Flint is skeptical.

"As late as it's getting in the season, it's getting a little scary," Flint said. "If all the water comes at once, the reservoirs won't stop it."

Hillsides are saturated adjacent to many streams and irrigation canals. Should a major slide occur during runoff, even a fast clearing of the channels won't prevent some flooding, he said.

"If there's a mudslide into a canal, we could have a real problem," he said.

Why is all this happening?

Alder said soil water levels were high the last couple of springs, increasing the chance of landslides and debris flows. A landslide is when a large block of a slope moves; a debris flow is when heavy rain or runoff sweeps mud, rocks and tree limbs off a hillside.

"You've always got to be concerned when the moisture level is as high as it is," he said.

During the 1996-97 water year, Utah had unusually heavy rains and snowfalls. That season's total was about 157 percent of normal.

"It saturated the soils. We had more landslides in 1997 than we had seen since the wet years of 1982-84," Allison said. During that time the Thistle slide reactivated, and a new landslide developed a mile below Thistle.

In October 1997 the ground was still soaked. The soil should have been dry at that time, but "the landslides were still gushing water everywhere we went." Then the latest wet season began.

So far in the 1997-98 water year, Utah's precipitation has been close to normal. But because the previous summer was so wet, the soil may be unstable. UGS earth scientists are watching the landslide threat.

In the mountains, the winter snow has yet to melt, and new snowstorms are contributing to the snowpack. The danger is that all of the snow might melt at once with a hot spell or a thunderstorm.

If "all of that water comes down, hits into the areas that are already unstable or are on the verge of becoming unstable, we have the potential for a lot of landslides all over the state," Allison said. Debris flows and flooding are other possibilities.

Most dangerous areas for landslides this year, according to Allison, are a part of the Thistle slide itself and the Shurtz Lake slide.

Clyde Naylor, Utah County engineer, said crews periodically take a look at the Shurtz Lake landslide. "Right now it's not affecting a great deal and probably won't," he said.

The Shurtz Lake slide already has moved power poles out of align-ment, Naylor said.

If the slide does reach the river, he thinks the river would just move a short distance around it and continue flowing.

Geologists are also concerned about a slide near Chalk Creek that developed in May 1997 east of Coal-ville in Summit County. If that slide reaches the creek it might dam the water and flood homes and cabins in the area.


Additional Information

Utah snowpack 1998

Bear River Basin 118%

Weber-Ogden River Basin 129%

Utah Lake/Jordan River 122%

Tooele Valley/Vernon Creek 171%

Green River 141%

Duchesne River 118%

Price River/San Rafael River 117%

Dirty Devil River 119%

Southeastern Utah 195%

Sevier River 141%

Beaver River 154%

Escalante River 160%

Virgin River 167%

Brighton 127%

Snowbird 126%

Parleys Summit 102%

Ben Lomond Trail 239%

Ben Lomond Peak 149%

Farmington 162%

Little Bear River 214%