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The Pittsburgh area is prone to landslides, and human activity often makes them worse down town

Monday, August 06, 2001

By Don Hopey, Post-Gazette Staff Writer

When the earth moves, sometimes it's not a good thing. Cynthia Lum knows. About 50 feet of her backyard in Rosslyn Heights no longer lives up to that geographic name, having tumbled down a cliff in a landslide that began after heavy rains this spring.

The landslide also pared off the backyards of two of Lum's neighbors and new fissures continue to open as you read this, indicating the earth is not done slipping and that more of their yards, and even their homes, could be lost.

Joe Miller knows that sinking feeling. The backyard of his Janey Drive home in Baldwin Borough is slipping downhill to Doyle Road. The slide has taken his swimming pool, a cabana, deck and two doghouses. (Darrell Sapp, Post-Gazette)

"When people buy a house they ask about the number of bedrooms and baths and garage space, but not what's under it," said Lum, who purchased her home last November without knowing it was built on fill material.

"The deed showed the house was 20 years old and I thought the property and adjacent hillside were stable. It never occurred to me as a home buyer to find out what my house was built on. I thought they'd be where they were forever."

Lum is not alone among southwestern Pennsylvania homeowners in that kind of thinking -- or in lamenting the disappearance of land lost to slides.

Because of natural geologic conditions -- steep hills and soft and slippery underlying rock layers -- the region is one of the most landslide prone areas in the country.

And the widespread re-grading and filling of hills and valleys for housing and business development over the past 50 years, plus the use of large excavating equipment to slice through hillsides for roads, has made the problem worse.

Know your slides

Those worried about homes or businesses slipping away have very few places to get information about landslide risks, but help is on the way.

The Pittsburgh Geological Society will start work tomorrow assembling a new Web site -- www.pittsburghgeological
-- that will post aerial photos identifying slide-prone areas in Allegheny County.

"When it's in place it will be the best place for home buyers and property owners to check to determine if their properties are in slide-prone areas," said Judy Neland, a society member.

Neland said the Web site will use high-resolution aerial photography of the region done in the 1970s by the U.S. Geological Service to identify landslide areas. Plans are to overlay a map of Allegheny County and mark each landslide, including recent ones.

"If each landslide gets a dot, a pattern will become apparent as to where landslides have occurred and are likely to occur," she said. "Some municipalities will have lots of dots and they will raise questions and maybe start to educate themselves on development and land-use policies."

The state Department of Conservation and Natural Resources is also planning to start a state-wide landslide database, said Helen Delano, a geologist with the department's Bureau of Topographic and Geologic Survey.

"We're working on one, but there have been questions raised about spending tax money on landslide reporting when the state has no regulatory oversight and offers no assistance to those whose properties are damaged," Delano said. "Certainly I see such information as a need."

Currently, the best sources for information about landslide-prone areas are county or municipal government offices, all of which received landslide maps from the state's Bureau of Topographic and Geologic Survey several years ago. The bureau's regional office on Washington's Landing also has the maps, but in the wake of media reports about local landslides its small staff can be overwhelmed by information requests.

-- By Don Hopey


Landslides have caused backyards, side yards and sometimes homes to slip away in Rosslyn Heights, Baldwin Borough, Troy Hill, Brentwood and Shaler. They've also blocked many roads in the region.

Because most landslides move slowly, they usually cause property damage rather than injury. And because most are of the "backyard slide" variety, are scattered widely around the region and affect just a few property owners at a time, they don't usually attract the attention afforded other geological hazards -- earthquakes, volcanoes, floods and subsidence -- that are more concentrated in their devastation.

But local landslides can be dramatic or even deadly:

In 1942, a rock fall buried a bus near Aliquippa, killing 22 people on board.

In 1951, excavators for a new office building made an eight-foot deep cut at the base of a hill along Island Avenue in Stowe, triggering a 500-foot wide landslide that destroyed six houses, covered the road and dislocated a streetcar line and various utility lines.

In 1983, a rockslide killed two people who were sitting in their cars at a traffic light on Saw Mill Run Boulevard.

"It's a problem people should be well aware of and it always seems strange to me that, as many times as landslides occur around here, people are surprised," said John Harper, chief of the subsurface geology section for the Pennsylvania Geological Survey.

Harper said it's impossible to predict if or when a slide will occur, but a variety of human actions -- including filling, digging or building on a hillside -- contribute to making them happen.

"Why landslides occur where they do and when they do is a tougher question," he said. "The safest answer is gravity."

Sliding through the ages

Land has been answering to gravity in Western Pennsylvania on a regular basis since the last Ice Age.

U.S. Geological Survey landslide inventory maps of Allegheny and Washington counties document more than 15,000 ancient and geologically recent major landslides. In one small, movement-prone section of Greene County, a USGS map identifies more than 2,100 landslides.

Native American tribes acknowledged the local landscape's unsteady nature. They called the river now known as the Monongahela the Menaungehilla, which means "river with the sliding banks," or "high banks that break off and fall down."

Such earth movement happened then and happens now because in many places the bedrock consists mainly of soft shales and claystones that weather rapidly when exposed and become slippery when large doses of water from snowmelt or spring rains are added.

The so-called "Pittsburgh red beds," a 40- to 60-foot thick layer of mostly reddish, greenish and grayish claystones and shales are the best known among the highly mobile bedrock layers, but there are many others.

Combining that geology with the region's steep topography is a sure-fire recipe for slides, according to Helen Delano, a geologist for the state Bureau of Topographic and Geologic Survey.

"Southwestern Pennsylvania is more prone to landslides than other parts of the state," Delano said. "Washington and Greene counties actually have the highest occurrence of landslides, but there are not as many people living there as in other places so they're not as costly.

"The greater Pittsburgh area has the biggest problem with landslides when you factor the human element into the equation."

Judy Neland, vice president of the Pittsburgh Geological Society, said newer housing developments often are built on slopes or on ground leveled with fill that, if not properly anchored and buttressed, can eventually give way.

And she said the municipal zoning boards that approve building proposals may not have the authority or expertise to restrict building in geologically marginal areas.

"That comes under the heading of land use planning and that gets people hot," Neland said. "But we are now pushing the envelope on where we build and any limitations can affect property owners, builders and even a municipality's tax base."

A lack of numbers

Despite the area's landslide history, geological ripeness for future occurrences and recent land development, no one knows for certain how many landslides occur each year or how much damage they cause.

"I don't know if we're having more now, but we're having more than in pioneer days when they mostly built on the floodplains and few people built on the hillside slopes because they were too steep," Harper said.

"If you look around Pittsburgh at the building done over the last century you'll see hillsides covered with houses, many with two-story fronts and five story backs. It's a wonder there haven't been more instances of landslides affecting those."

A 1986 study identified more than 700 recent and active landslides in Allegheny County, and the state Department of Transportation's latest review, now 10 years old, listed 226 problem landslides along roads in Allegheny County, 45 in Beaver County and 77 in Armstrong County.

PennDOT also estimated in 1991 that an average of $10 million per year statewide was spent on landslide repair contracts and a similar amount in landslide mitigation and grading costs.

Bill Adams, a PennDOT geotechnical engineer, said more recent cost estimates aren't available, but among the new and expensive efforts to prevent or mitigate landslides are the flexible, energy-absorbing fences installed at trouble spots along Saw Mill Run Boulevard near the West End Circle and below the Boulevard of the Allies near Duquesne University.

"There are 100s of landslides and rock falls affecting roadways and people's properties every year," Adams said. "After a snowy winter and wet spring we see more of those on state roads and the same thing is happening on municipal and county roadways."

Landslides aren't covered by homeowners insurance policies because they're deemed "acts of God." And unlike floods and subsidence, there are no state or federal insurance programs to bridge that coverage gap.

So when "backyard landslides" do occur they can be devastating for individual property owners.

Periodic legislative attempts over the last 30 years by Western Pennsylvania legislators to address the landslide insurance issue have failed to attract support in the General Assembly because it is perceived as a regional problem.

State Rep. Don Walko, D-North Side, said last week he would re-introduce legislation to establish a new committee to conduct public hearings on the landslide issue and propose legislation.

Adams said that after numerous landslides triggered by Hurricane Agnes in 1972, an ad hoc legislative committee recommended that the state take an inventory of landslide-prone sites, fund some type of insurance program to help individuals affected by them and couple it with land development regulations.

"It has to be a package, the insurance funding and the land-use regulations, or the program could be bankrupted by continued building in unstable areas," said Adams, who worked with the committee. "And there are lots of vested interests, like the insurance industry, banks, real estate industry, developers and municipalities, to deal with too."

Property damage

In Shaler, a landslide sheared the edge off a 30-year-old housing development three years ago, sending backyards tumbling down a ravine and exposing the foundations of two houses, one of which the homeowner moved at considerable expense to a more stable lot.

The slide also caused the township to close Stoneridge Park when debris covered a 30-foot-tall waterfall and backed up the small creek. Over the past two years the waterfall has re-established itself, the creek is flowing and people are using the park, but it remains officially closed.

In Brentwood, three homeowners along the low side of Bel Air Road have seen their backyards slip considerably lower. One had to fill an in-ground swimming pool that now sits on the edge of a steep drop-off.

On Janey Drive in Baldwin Borough, the backyards of three homes have been sheered off by a slide that started in March. The slide has taken a swimming pool, cabana, two dog houses and a shed more than 100 feet down a steep hill and halfway to Doyle Road, which has been closed several times because the slide has blocked one or more lanes.

"One day we just saw a crack in the corner of our driveway and the next day it just dropped," said Virginia Sciulli. She and husband, Fred, are the original owners of their Janey Drive home and have lived there for over 30 years.

The Sciullis, like Lum and her neighbors in Rosslyn Heights, aren't getting much more than sympathy from municipal officials. The homeowners are facing home repair and property stabilization costs that could easily reach $250,000 per landslide.

"I have bought a problem and it's a nightmare," Lum said. "We're trapped and can't move because we can't sell. Fixing the damage is our responsibility but homeowners insurance doesn't cover it.

"It's an insurmountable problem that's not of our making and that's the horror of it."

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