Pennsylvania Landslides, Pittsburgh and Beyond: A 40-year Perspective

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Detailed Description

A broad overview of landslide geology across Pennsylvania, and historical and current work on landslides by the Pennsylvania Survey and others. The diverse geology and topography of Pennsylvania's woods provides a variety of landslide problems beyond the well-known issues around Pittsburgh.


Date Taken:

Length: 01:02:52

Location Taken: US

Video Credits

Lisa Wald



Okay, folks. My name is
Matt Thomas, and thank you

for tuning into the USGS Landslide
Hazards Program seminar series.

For folks that are new to this meeting,
you have the ability to submit questions

via the chat window or to use
the raise-your-hand feature

in combination with your
microphone and video camera.

We typically wait until the end of
the presentation to take questions,

but feel free to enter them in the
chat window as the talk progresses,

and then we can address
those questions at the end.

In the meantime, please just do
your best to make sure your

microphone is muted when
you’re not intending to speak.

I’d just also like to note that today
Helen is our kind of second speaker

in part of a new miniseries
where we hope to hear from

one state survey each month.
These talks are intended to provide

an overview of the program,
including expertise, focus areas,

and product types and introduce
some of the more pressing

landslide-related problems
that that state faces.

If you’d like to have your state
landslide work spotlighted as part of

this miniseries, just please just shoot
me a message via Teams or email

and we can coordinate a date. Jaime,
I’ll go ahead and turn it over to you.

- Okay. Thanks, Matt.

Helen and I are former colleagues
at the Pennsylvania Geological Survey,

and it’s really my pleasure
to introduce her today.

Makes me nostalgic looking at
her photo on the title slide.

Helen was raised on Cape Cod, which
sparked an early interest in geology,

particularly coastal geology.
She received her bachelor’s from

Tufts University and a master’s
from SUNY-Binghamton and,

following her master’s,
worked for a short time

for the National Park Service at
the Cape Cod National Seashore.

Helen joined the Environmental
Geology Division of the

Pennsylvania Survey in 1980.
At that time, she was the only

non-oil and gas person working
at the Survey’s Pittsburgh office,

where she worked on Lake Erie coastal
issues, general western PA geology

inquiries, and landslide hazards.
In 1989, Helen moved to the main

Survey office, which is located
in Harrisburg, where she has worked

on a number of different things,
including siting critical facilities,

Lidar acquisition, GIS,
local government outreach.

She’s always remained the main
point of contact for landslides

for the entire Survey, whether
in Pittsburgh or in Harrisburg.

She’s currently working to wrap up
some landslide inventory work

and, after more than 40 years at the
Survey, is contemplating retirement,

but no official plans yet.

So, Helen, the floor is yours.
- Thanks, Jaime.

I’m going to switch over to
presenter mode and …

There we go.

Have you got the big screen yet?
- Not yet.

- There. How about now?
- Yep.

- You’re good to go.
- Okay.

As Jaime said, I have been
kicking around Pennsylvania

for a little over
40 years now.

And, for most of that time, I have
been the part-time landslide program.

We heard from the nice folks at the
Washington Survey, and I’m envious

of their seven full-time equivalents.
We’ve got one part-time equivalent,

but maybe we make up for it
by longevity. We’ll see.

Anyhow, most of you are probably
somewhat familiar with Pennsylvania

landslides from a Pittsburgh viewpoint,
but most of you, since I see that this

crew is largely a western group,
may not know a lot about

Pennsylvania or the Survey.
So I’m going to tell you

a little bit first, and then we
can look at some landslides.

So, like many state geologic surveys,
we are in our government.

We are not tied to a university.
We’ve been around since 1836.

Our legislative justification
is pretty broad.

We are charged to go out and
study the geology and make it

available to the public.
There is no specific mandate for us

to do geologic hazards work, but it
certainly is allowed under our umbrella.

At the moment, we have
a full staff of 31 positions.

As you can see from the red lines,
we’ve got a number of – a number

of folks who have recently retired.
We are generally a crew of

senior citizens. About half the staff
could retire tomorrow without notice,

but we hope they’re going
to hang in a little longer.

We’re in the process of filling all
but one of these positions right now,

so we should be back to
full complement pretty soon.

COVID was a little rough.
There were hiring freezes.

But those have been lifted,
and we’re now moving forward.

Survey has three divisions of
geologic mapping, which I man

in the groundwater and
environmental geology section.

We have conventional field mappers,
a couple groundwater folks,

my counterpart who does [inaudible]
stuff, and a surficial geology mapper.

The economic resources division
is heavily oil and gas and mostly

in Pittsburgh, but we have
a small group in Harrisburg

who run the scanning electron
microscope and the x-ray stuff

and look at economic minerals
and [audio cuts out] in general.

And we have a GIS
and geoinformation section

that does our publications –
GIS work.

We have an actual full-time
librarian for our paper and

some electronic resources.
And we have a core and cuttings

library with a full-time
custodian who is a geologist.

And the usual
administrative staff.

We used to have in-house IT people,
but they’ve been lifted and put into

an umbrella over
other state agencies.

So we do have IT support,
but they’re not our employees.

So onto what
Pennsylvania looks like.

Unlike your western mountains,
we don’t go that high, but we do

have some relief. Many of you have
seen this in your intro geology classes.

We have the folded Appalachian classic
linear mountains, where the sandstone

ridges hold up the sky and the karst
and shale valleys in between.

The Allegheny Front here is the
break between the folded mountains

and the Appalachian plateaus,
where the rocks are basically flat-lying,

although there are
some general wrinkles.

For landslide purposes,
we’re going to ignore everything

south of the first ridge here at
Blue Mountain because the

Mesozoic basin would
have landslides if it had

any topography in the red shales.
And the Piedmont, similarly,

doesn’t have enough topography to
have significant landslide issues.

So we’ll be looking at the other parts
of [audio cuts out] primarily.

The colors in this – the white
areas are above 2,000 feet.

The green is below 500.

The yellows and
browns are in between.

Highest point in Pennsylvania,
Mount Davis, is down here

in the southwest, about here.
Pittsburgh is here.

You’ll be seeing more and hearing
about it where the Allegheny and the

Monongahela Rivers come and make
the Ohio, which goes out there.

Philadelphia, for sports fans
who care about that, is over here.

I notice my laser pointer
is not moving very well.

There you go.

Geographic provinces –
I alluded to those, but they

have official boundaries.
We’ll talk about some of that.

Most of that showed up in
the other [inaudible],

but just to show we do
worry about these a little bit.

You USGS folks will recognize
the classic colors of geologic

map formations by geologic age.
We have the Great Valley here

with Cambrian and Ordovician
carbonates and shales.

We hit the Silurian with Tuscarora
sandstone at the first [inaudible]

or Blue Mountain.
And we move up through Silurian,

Devonian, Mississippian,
Pennsylvanian, and to a little bit

of Permian in the
southwest of the plateau.

In Pennsylvania, because everything is
Paleozoic except our small Mesozoic

basin, these colors get boring.
So our geologic map looks like this.

But, for those used to the classic
colors, it’s a little disconcerting.

This does add detail, and you can
see that there are some gentle folds

here in the eastern edges of the
plateau coming off of the

compression from the
really wrinkly mountains.

Things that we’ll be looking at.
In southwestern Pennsylvania,

the yellow formations, Conemaugh, are
some of the bad actors as well as

the continuing shales and things.
These are deltaic and terrestrial

sediments for the most part with
occasional marine incursions.

Lots and lots of clay.

Some fluvial sandstones interbedded.
They’re cyclothems, so there’s lots

of small-scale variety within
the formations, which makes it

a little tricky to pick out where the
landslides are most likely to be.

But the bad actors are commonly
some paleosol units in the deltaic

shales that have some interestingly
weathered clays that are the roots

of some of the landslide
problems in Pittsburgh.

In other parts of the state, the Devonian
and adjacent Devonian-Mississippian

units, which are also deltaic – this is
the Catskill Delta coming off

of mountains to the east and
shedding sediments off to the

west in the upper Devonian.
It also has both some volcanic ashes

and some paleosols.
Again, it’s very difficult to map

single units within it, so we don’t
have a good handle on those

specifically, and it has occurred to
me that maybe mapping landslides

would be a way to map where
some of those paleosols are.

But that’s a bigger task
than I’m likely to accomplish.

Structurally, things in the Ridge
and Valley are very steeply dipping.

There’s anthracite coal mining
in some of these basins to the east.

And rock standing
on end around here.

And we get over, there’s a
concentration of activity,

as you’ll see, along the Allegheny Front,
which is structurally understandable

when you realize that that’s
where the flat stuff is butting up

against the
really folded stuff.

There’s some interesting
things going on at depth

that the oil and gas
folks can tell us about.

But it means that some of these rocks
are more intensely fractured than

necessarily expected from just
their surface exposure.

So there’s your
basic geology lesson.

And then, in the Pleistocene,
we did get glaciated partly.

However, all of Pennsylvania
was subject to periglacial

intense weathering.
We’ve got gelifluction and solifluction

lobes all over lots of the mountains,
which we’re able to see now with Lidar.

But actual glacial deposits are limited.
The other important thing that happened

in the Pleistocene is that the river
drainage in western Pennsylvania

formerly went into
what’s now the Great Lakes.

When the first ice came down
in the early Pleistocene,

it dammed that drainage, backed up
a big lake, overflowed into what’s

now the Ohio River, and sent all
that water down to the Mississippi.

If you remember your fluvial
geomorphology, you’ll realize

that the Mississippi drains into
the Gulf of Mexico at sea level.

And Lake Erie is
at about 500 feet.

And therefore, those rivers have
been adjusting to a new base level

for the last couple million years,
and they’re not done yet.

So that’s the root of many of the
steep slopes in western Pennsylvania

is that the rivers had to downcut
an extra couple hundred feet,

and the middle and upper
tributaries are still doing so.

So my talented retired colleague
John Harper drew this cartoon

as the cover of a guidebook for the
Field Conference of Pennsylvania

Geologists about two weeks after
I started working at the Survey.

And it nicely summarizes what’s
going on with Pittsburgh geology.

You’ve got interbedded sandstones
undercut by weathering shales.

The weak red bed paleosol
claystones. Valley deepening.

And, as the valleys deepened,
vertical stress relief fractures

tended to form along those
valley sides, which led to

some big bedrock slides,
which can get reactivated.

Periglacial and postglacial
weathering of clay-rich rocks

has produced some very thick
colluvial soils on lower slopes.

There are the usual bedrock
discontinuities of fractures

in bedding planes. We [audio cuts out]
some good-sized rivers on it,

and then we built a city.
And then we mined the coal.

The coal actually has very little to
do with landslides, but the general

public would love that it would
because there’s insurance for

coal mine subsidence,
and there is not insurance

for landslides, as most
of you probably are aware.

So Pennsylvania Survey’s
history with landslides.

In the 1960s, the oil and gas folks
in the Pittsburgh office were asked

to assist the highway department and
some municipalities with some local

landslides relating specifically
to some major highway

development around Pittsburgh.
They assisted with general

geologic information, x-ray
identification of clays, and so forth.

But we didn’t have a thing
approaching a formal program.

In the 1970s, everybody
got environmentally aware.

Pennsylvania created a Department
of Environmental Resources,

and the Survey
was moved into it.

We created an Environmental
Geology Division.

And one person
was sent to Pittsburgh.

Also, at that point, a consortium
of the U.S. Geologic Survey,

the Pennsylvania Survey, the
Appalachian Regional Commission,

and a bunch of other agencies
developed a project called the

Pittsburgh Regional
Environmental Geologic Study.

I think there were some other
similar ones in other major cities

around the country
at the same time.

I believe Cincinnati had one and
probably some western ones.

But this was a major effort to look
at environmental geology in the

six counties around Pittsburgh.
They produced a new 1-to-125,000

geologic map, mapped coal mines,
mapped floods, produced slope maps,

and started making
landslide maps.

The two major players in landslide
maps were Jack Pomeroy and

Bill Davies, both now deceased,
but they were good folks.

Did a lot of good work.
They used aerial photos and some

field checking, produced
7-1/2-minute quad-scale maps for the –

for Allegheny County showing old
landslides, new landslides, features

they thought were related to landslides,
and coal mining features. And fills.

There’s a USGS circular you can
look up that details some of that

work and talks about it.
But those maps were well-received.

Although, as we’ll say later, not as
well used as they might have been.

And so the quad-scale landslide
mapping program was expanded and

included most of western Pennsylvania
in the pink and red areas shown here.

And also extended into other states
all down the Appalachians.

They produced, in Pennsylvania –
I think it’s about 380 quad maps.

As a cooperating agency, the
Pennsylvania Survey is a repository

for those maps, and we got stacks of
mylar reproducible copies of them.

The originals were hand-colored
on paper topo maps.

We got photocopied
mylar reproducibles.

And, if you want to look at some of
those, you can still find them through

the USGS Open-File
reports program.

But we have scanned PDFs
available on our website as well.

Again, they were done
with aerial photo interpretation.

And, unlike the Allegheny County
group, which had some very nice

low-elevation photos flown, this used
whatever photos already existed.

So they vary considerably.
But it’s a good effort,

and the maps have been useful.
They’re not perfect, but they’re

pretty darn good, and especially
in the area around Pittsburgh

and southwest,
remarkably still useful.

As part of this larger project,
they also chose several specific areas

for more detailed studies.
There are a number of USGS

miscellaneous field studies
and miscellaneous investigations,

reports, that came out of it.

They looked at some areas around
the glacial border up in Warren.

They looked at some things in East Brady
up here in Armstrong County.

They looked at some sites in
Washington County that were in

coal mining areas. And they looked at
a quad down here in Green County.

So those maps are available.
And they did some

now-seemingly-simplistic looks
at mapping by slope or mapping

over dip-slopes looking at things.
But it was a good start.

The best summary of some of that work
is Jack Pomeroy’s USGS Professional

Paper, number 1229, and I’ll send
you a link to that later in the chat.

Here’s what some of these look
like now laid over Lidar data.

This is a section
in suburban Pittsburgh.

The Lidar laid over an orthophoto.
It’s fairly straightforward.

You can see nice, flat-lying bedrock
flat up on surfaces, flat belly bottom,

and steep everywhere in between.
The red stuff is the information

from the USGS maps. So solid red is
what they perceived was an active

landslide when they were mapping.
These cross-hatched areas are

older landslides. And the stippled
area that will be hard for you to see

is soil and rock susceptible to
landslides, which was basically

laid out by looking at where
the old landslides occurred.

Now, here in Allegheny County,
you’ve got, I’d say, clay-rich soils,

lots of colluvium on the slopes.
Maximum relief of 400 feet.

So, you know, we don’t have big
mountains, but we do have steep slopes.

And we have
a city built on it.

Here is another example
near Pittsburgh –

actually, in the
city of Pittsburgh.

They turned old city street in this valley
bottom into what’s now Interstate 279

and cut through the toes of
quite a lot of old [audio cuts out].


… so this is suburban Pittsburgh.
You can see – I can’t move my mouse,

but you can see flat-lying
sedimentary rocks,

flat up on surfaces, flat creek bottom.
And the red overprint

is the information from
the USGS landslide maps.

So let’s go to the next one.
This is similar – different way

of graphically showing it.
This is in the city of Pittsburgh,

where they took an old road through
the bottom of the East Street Valley

and turned it into an interstate.
This is Interstate 279 on the

north side of Pittsburgh. And the red –
dark reds are active landslides.

The pink were
old landslides.

The green was soil and
rock susceptible to landslides.

Folks used to looking at Lidar
can probably pick out many of

the landslides on the slope,
but it’s also interesting that

all the new highway construction
has obliterated some of those.

That got kind of complicated
and expensive as they were building

the highway and had to
move rather a lot of material.

Next slide.

This is in far southwest Pennsylvania,
and the guys making the USGS maps

didn’t quite believe the intensity
of landslides they thought they

were picking up on air photos.
So Jack Pomeroy spent three weeks

in one quad mapping in detail and
published a freestanding miscellaneous

investigations report.
And the red overprint is

the information from that overlaid
on a Lidar slope map for a small part.

So you’re further – you’re up into
the Permian and uppermost

Pennsylvanian rocks.
Thinner units, but you still have

alternating thin sandstones, shales,
claystones, thin coals, underclays,

freshwater limestones, and the
weather produced – it’s hard to

argue very thick soils when you can
see all those bedrock layers in the Lidar,

but the soils that are
there are pretty mobile.

So next slide.

So anyhow, after the USGS folks
decided they were done with mapping

in Pennsylvania, the Pennsylvania
Survey took on the project to

extend that to the next 1-by-2 degree
sheet east – the Williamsport report.

Pete Wilshusen from the Harrisburg
office and I got assigned to look at that,

and we spent a couple of years doing
air photos and field checking.

And he did mostly the east, and I did
mostly the west, but we collaborated.

And, for editorial reasons,
this didn’t get published

for a long time, but we have
this report, which is not bad.

There were a lot of things we
misidentified now that we can see

Lidar, but we probably overidentified
some things that are likely periglacial

features, but there are a lot of solid
landslides that we did identify.

We did not attempt to do a full
inventory of all 128 quads.

Because that would have not
been possible in the time span

we were given. So we did a statistical
sample of the quads, made sure we

covered all the typical types of
bedrock and surficial geology,

generalized the information
on landslide occurrences

to attempt a susceptibility map.
But we did publish reduced-scale

7-1/2-minute quads in the report
showing all of the slides we identified.

So this is, like all of our publications,
now available as a PDF and can

be downloaded from the web.
We don’t have any more paper copies.

We don’t do that anymore.
It got too expensive to shelve them.

So …

Oh, come on. Next slide is the
1-to-250,000 scale map

that came out of that report.
You can’t see the individual

black dots for the landslides,
but the darkest blue is what we

considered high, which – not high
compared to some other parts of

Pennsylvania, but high for this area.
Susceptibility, which was largely

the north-draining river valleys,
which are full of glacial lake clays

and other glacial sediments.
Some of the very dendritic valleys in

the western part, which are very steep.
The section into the Devonian

sandstones and shales – mostly shales –
in the high plateaus – unglaciated

section of the Appalachian plateaus.
And a couple of high mountain ridges

in the lower central area,
Bald Eagle Mountain, which is

sort of the last big sandstone mountain
before you hit the Allegheny Front.

And, over in the southeast,
the tail end of that sort of

what we call the anthracite
banana in the eastern section.

So I don’t know how much
use this map has ever gotten

and be used, but it’s out there.
And this is not a heavily populated area.

A lot of forest land.
A lot of farm land.

So it’s not a lot of development yet,
but there is some, and we’re hopeful

that this may be
a useful product.

So we have an education series
publication illustrated –

next slide, sorry –
illustrated over on the left here.

And the little map is the centerfold
for it, is just a real thumbnail based on

physiographic provinces of a sort of
high-medium-low – I would be

hard-pressed to defend some of these,
and I would put a higher zone down

in the far southwest, but the editors
wouldn’t let me have another color.

So this is out there as, again,
a sense of where there is

some landslide
activity in Pennsylvania.

Next slide.

Into the 21st century.
We are now moved into

a department called Conservation
and National Resources.

They split up the old Department
of Environmental Resources.

And the regulatory folks are
now in a different department.

So we get a different set of requests
from the public for support,

but we do get some requests
for assistance to municipalities

and individuals or of hand-holding of
individual homeowners with landslide –

we can’t fix anything,
we’re not engineers, but we can

counsel them on the types of people
they need to hire and so forth.

I’ve been collecting
media reports.

And, in this internet age,
that’s gotten a lot easier to do.

I can get newspaper or –
digital newspaper or digital

TV reports of lots
of landslide incidents.

Again, the Pittsburgh market is the big
area, but I pick up some others as well.

So I’ve been collecting
and saving those.

As a part of a data preservation effort,
I started looking at the old case files

from the 1960s to present and some
academic and published reports.

And I’ve been compiling
all of that into a GIS database.

I now have approximately
600 Allegheny County landslides,

all of which have a good location
within a couple of thousand feet at

most, sometimes very good locations.
And some sort of a date.

It may be the occurrence date.
It may be the report date.

But there’s some date that links to them.
Some of them have polygons.

Some of them have quite extensive
data on damages and causes.

Some have merely an entrance that –
entry that someone phoned us

they have a landslide,
and we put a dot on the map.

But there’s some information there,
and that is anticipated.

We’re working on plans as
to exactly how to release that.

We have IT issues, but I’m anticipating
that that will be available to go into

the USGS combined
inventory map and released

as a freestanding
database in some form.

I can’t tell you exactly how or when,
but it’s going to happen before I retire.

And, in the 21st century, we got Lidar,
which you all will appreciate.

So next slide.

I worked on this, as did Jaime,
but, in 2006 to 2008,

we acquired statewide Lidar.
Now lower res than we’d like.

It’s QL-3.
But it’s all the same resolution,

all the same tiling scheme,
and available free.

It has changed the way we do geologic
mapping, as you all can appreciate.

We were among the first states
to have statewide Lidar.

That’s no longer as big
a deal as it used to be.

However, we are moving to having
a second pass of QL-2 Lidar.

The black areas here are what’s
available right now to download,

and we anticipate that the rest of the
state will be filled in before the end of

this calendar year. The stuff has
been collected and is in processing.

So we should have two sets of Lidar,
and I’m actually looking forward to

seeing what happens when we
start comparing them and seeing

what happened in the
intervening 10-ish years.

So that is the summary of any
kind of a landslide program

that the Pennsylvania Survey has.
As I alluded earlier, it’s sort of

me half-time or thereabouts.
And obviously, the Lidar is

a huge issue. I worked on it
in the early years.

Now it’s a consortium.
USGS is managing the project.

And we’re doing other
things with it as well.

But that is what we’ve got for anything
that can qualify as a landslide program.

But now I’ll show you
some bells and whistles

and a few things that
we’ve learned about.

After the Oso Washington event,
we thought we might get questions

about whether anything similar could
happen anywhere in Pennsylvania.

And we had statewide
Lidar, so I took a look.

I took known large landslides –
and I’ll show you a couple of them

in a bit – and I did a visual scan of a
statewide slope layer projected at

1-to-24,000 and looked for large slides
that I could see on a Lidar slope map.

I found around 100, 120,
that seemed large.

But, when I looked for a way to screen
them, I pulled a number out of the air

and screened off an area of a million
square feet and found we had about 38.

About half were in bedrock and
half were in glacial deposits in

northeastern/north central Pennsylvania.
And none of them were in western

Pennsylvania, which is what
we think of as landslide country.

So here is the map I used in
a GSA poster presentation.

The red boxes were callouts
to specific information about

some individual landslides.
And we’ll look at a couple of those,

and then I’ll take you on
a tour of some other landslides.

I think the limiting factor to keeping
us from having large landslides

is that our hills aren’t high enough.
We have what we call mountains.

Most of you would – from the west
would laugh at them as mountains.

But they certainly were a barrier
to historic transportation,

and they’re pretty, and they’re lovely.
They do have trees on top of them,

for the most part. But they are a
significant topographic feature in

Pennsylvania and, as you’ll see, they
have some pretty good landslides.

Next slide.

This is, I believe, the largest –
I know is the largest known

landslide in Pennsylvania.

It’s on a bedrock dip slope,
dipping southeast, and Devonian

and Mississippian sandstones
with some shale interbeds.

Along this flank of the mountain on the
north branch of the Susquehanna River,

just southwest of Scranton and Wilkes-
Barre, there are a whole row of these.

There are perhaps a dozen,
all smaller than this.

Most of them didn’t run out onto
the flood plain, at least not yet.

On the left, you can see an orthophoto,
and you can see why, perhaps,

we didn’t pick it up on air photos as a
landslide in the Williamsport mapping.

That was not an area we were
statistically assigned to do,

but we did pull in some
other things we knew about.

But, on Lidar, it shows
up rather dramatically.

It’s about – it’s almost
4,000 feet across.

And, according to Duane Braun
and a couple of other colleagues

who published in a GSA special paper,
they believe this whole series of

slides are post-glacial,
but probably haven’t moved

significantly in
more than 4,000 years.

You can read the – read their rationale
for that. I’ll provide the reference later.

But they do still show signs of
looking kind of fresh and active,

but there’s nothing creeping out at
the toe, no discernable movement.

And, believe me, the folks in the county –
emergency management folks know

about them and are paying attention.
So, however, I strongly suspect that,

at some point, this may
have blocked the whole river.

And, if it should move again,
it would block the river again

and Scranton and Wilkes-Barre
could get a little damp.

This is one of the other slides in
that series along the mountain.

You can see the size and nature
of the mountain and a cross-section

from Duane’s work. A simple block
slide on a bedding plane surface

on a mudstone layer with some
glacial deposits on the toe that got

distorted a bit. But they’re not the
primary moving force in the landslide.

We assume the other slides along
the mountain front are pretty similar.

Next slide.

Are we on to Torbert now?
- The picture I – oop.

Helen, the picture I see is a cross-
section of mudstone, sandstones,

glacial deposits, and the – you know,
it’s a cross-section of the slide mass.

- Okay. I had just been
talking about that. I’m sorry.

I forgot to tell you to advance.
So now go to the next one.

- Okay.
Now we’re on Torbert.

- Okay. This is another one of the
very large slides that we picked up.

Pete and I did find this in
the Williamsport report.

Pete had gone and called out
to talk to a homeowner in 1978.

And, if you look in the little
black-and-white map in the upper left,

there’s a little debris flow outline.
And that little debris flow knocked the

porch off a house, but didn’t do much
other damage, right at the very toe.

And he knew about it,
and so it was within the report area,

so we went to look at it. And we
hiked up the debris flow drainage.

And, when we got to the top,
we realized that there was

a whole lot more going on
up there than we had been aware.

Now, the graben across the top of this
is shown on the Pennsylvania

State Geologic Map as a fault.
Fellow in 1960 picked it up on the

air photos and mapped it that way.
But Pete and I looked pretty hard

on both sides and couldn’t find
any evidence of it coming around

the other side of
the hill as a fault.

So we think it’s just
this big rock slump.

And you can see that,
in the gully of the debris flow,

that it’s scoured down to rock, but
I now would not call that bedrock.

I think it’s probably moved
as part of the landslide.

And, over on the right-hand side, you
can see what it looks like on Lidar.

The colors are just
an elevation gradient.

And I drew a couple of
cross-sections and profiles across it.

So clearly was a whole lot more
than we could discern through

conventional aerial photo
interpretation and even hiking

up to the top and walking around.
We spent two or three days on this,

looking at it, but that was about all we
had time to do as part of the project.

But, again, it doesn’t seem to be
moving actively, although there’s

some stuff brewing off the
south edge there in the low –

bottom of the photo
that looks fairly fresh.

I don’t know that the big block
is likely to move, but if it does,

it’s going to kind of mess up the
flood plain of Pine Creek,

and there are some houses down
there and a fairly well-traveled road.

This is a forested area, but lots
of hunters and fishers and vacationers

go up there. And there aren’t
a lot of roads in this country.

They all tend to follow
the stream valleys.

And, if you block one,
it can be a pretty long detour.

So next slide.

We have – do not have the kinds of
big debris flows that the North Carolina

folks get in their big mountains
where you get a debris flow

coming down the mountain
or that you’ve got in Colorado

recently blocking up I-70.
But we do have some debris flows.

This is, I believe, the oldest reported
debris flow in North America.

I’ve asked a lot of people, and nobody’s
seemed to come up with one later.

There are some older landslide reports
up in the Saint Lawrence Valley.

But, in 1779, David Rittenhouse,
who was a Philadelphian of some note,

heard about this thing and rode his
horse over to look at it and was so

confounded by what could have caused
this great gash down the mountainside

that he wrote to his friend Benjamin
Franklin, who, at the time, was in Paris,

asking whether or not there could be
an electrical explanation for

why sandstone bedrock at the
very top of the mountain was

scoured out in a bowl and all
the stuff flowed down the hill.

Backing up and explaining,
the left photo orthophotography

shows that you can’t see much
with – through the modern forest.

My husband and I read about this
in a local historical society journal.

Somebody was editing Franklin’s
papers and came across this letter.

So we went out to see
if we could find it.

I looked at all the conventional air
photos – this was before we had Lidar –

and found one set of photos that had
a shadow that showed what might

have been an appropriate groove,
and we had some interesting

adventures getting to it
and finding it, but we did.

We convinced ourselves and other folks
that it really was this particular event.

And then, later, when we got Lidar,
it was a good excuse to play with

different blending
angles on a hillshade.

You can’t show a groove on the
mountain when the mountain runs

northeast-southwest with
a northwest-lighted hillshade.

But this is a southwest sun angle,
low-angle hillshade, and it shows up

the groove down the
mountain beautifully.

I can’t show you with the cursor,
but if you follow the red arrow

down the straight line into the
little stream valley, and then along –

this debris flow moved
into the stream valley and

down a total of about 4 miles to
the larger stream in the valley.

And the red dot on the geologic
map is the location of that.

It’s on Blue Mountain –
the first Tuscarora sandstone

mountain on the north
edge of the Great Valley.

We do still get some
of these more recently.

Next slide.

Sorry. Do you have
a Lidar image on it?

I think I was doctoring up the slides,
and I may not, but this was …

- Hi, Helen. Yeah. You’re on
Cowans Gap State Park debris flow.

- Yep.
- And it starts – it’s got a hillshade, yep.

- Yep. Okay. Well, that hillshade
was supposed to fly in later,

but it won’t do it on your version.
So anyhow, the left photo shows a view

down the channel, and the right photo,
partly blocked, shows some sandstone

blocks piled up against some trees.
But you can see at least the

bark scoured off the trees.
And you can see the Lidar image.

Cowans Gap is a state park west of
Harrisburg in the folded mountains.

Again, this is Tuscarora
sandstone bedrock.

Nearly vertical. The tip
of the red arrow is a ridge top.

In this case, the sun angle and
the hillshade is from the northeast

to show the debris flow.
But it’s remarkably similar to the

Carlisle Deluge in nature and scale.
Debris levees, scoured out hole.

Not quite at the top of the mountain,
but close to it. Straight down chute.

In this case, it jumped across a state
park road and through a urban –

a rural disposal dump where
folks had dumped their trash,

but spread said trash out through
the campground down below.

And eventually, some sediment
got into the state park lake.

So we don’t get a lot of these
actively, but we have a list,

and there are some,
and we obviously do get them.

But it’s not a problem because
the size – our mountains is such that –

and we don’t have the valley network
that folks further south have in the –

in the Blue Ridge, where you get the
Hurricane Camille and so forth and

things that the North Carolina
Survey has to worry so much about.

So there certainly is development
pushing into these mountains.

Used to be just hunting
camps and state parks.

Now more people are moving out there.
It’ll be interesting to see, with COVID,

whether people who want to work from
home are going to move out rurally.

But it’s not a huge problem for personal
safety, but we do have some of it.

So next slide.

Up in northeast Pennsylvania and
north-central, as I alluded in the

Williamsport map, we have valleys
full of glacial lake sediments.

Here, probably me excavating a sample
up on the hill slope below a scarp.

And, on the left, a 6-inch
ruler showing the varved clays.

And, if you go to the next slide, again,
this one was supposed to be one that

would sail in, but if you have
the Mansfield Quadrangle?

In the Lidar image?
- I’m looking at – Helen, I see – we’re

on glacial lake clay slumps, and it says,
“Tioga County, Pennsylvania.”

- Yep. Do you have an image,
or have you just got the words?

- Oh, we have the image as well.
- Okay. So you’ve got a Lidar image

with some red stuff over it.
Okay, these are – some of these

mapped, and the red overprint
is the mapping we did for

the Williamsport project.
So you can see some of these are

pretty good-sized, but they’re all along
the stream banks and [inaudible] up.

The next slide will be on a road that
is in the west-central part of this

Lidar image, as well as a view down
the stream valley. So next slide.

Glacial lake clay slumps.
A view of the stream valley

with the whole right-hand side of that
stream bank is slumping being actively

removed by stream erosion.
And the road has a head scarp in it.

And these things move pretty
continuously but pretty slowly,

and, at least in the 1980s,
the highway department’s attitude was,

it was not dangerous enough to need to
do anything more substantial, and their

approach was that they would just
keep repaving it every couple of years.

Clearly about time to
do that again in this photo.

But the uphill side of this road
probably has approximately

normal thickness of roadbed,
and on the downstream side,

you’ve got a whole lot
of built-up layers of asphalt.

So this is, again, a rural area.
This is a state highway and gets

some traffic, but there are largely
agricultural land and, you know,

the cows aren’t going to get too upset.
And these things are not moving fast.

But there are lots of them scattered
around in north-central Pennsylvania.

And, in a little bit, I’ll touch on a reason
that I’m fairly worried about them.

So next slide.

This was the image behind the
title slide just to show that

we do get some other things.
This was a recent –

November 2020 – bedrock slide.
Believe this is – I haven’t been to visit

it, but I believe it’s a bedding plane
failure in some of the Silurian shales.

That’s the – you’re looking west
along U.S. Route 11 near Danville,

if you know Pennsylvania, and that’s
the north branch of the Susquehanna,

not too far above where it joins
the west branch and turns south.

Took about a week for the
highway to be re-opened on that.

And it was a long detour to get around.
Again, this is a place where the roads

pretty much run in the valleys, and
there – it can be a long way around.

Next slide.

I would be remiss if I don’t touch
on the Lake Erie shoreline.

I know Matt has been
up there not too long ago.

We don’t generally consider this under
our landslide program, but I’ve spent

some time in my early years
at the Survey working up there.

And we really should.

The lake is constantly
eroding the high bluffs.

The bluffs, through most of the
47 miles of Pennsylvania’s

Lake Erie shoreline, are steep –
60 to 150 feet high.

Bedrock, glacial sediment contact
is pretty close to lake level.

It fluctuates up and down a bit.
The tills are, again, an irregular surface.

And then on top of the tills are
lacustrine deposits from previous

high stands of the proglacial lake.
So you get these gravels

and fine sands
and silty sand mixes.

You can see that the cliff swallows
really like that silty sand for nests.

And, for the same reasons,
this stuff is susceptible to piping.

So you get – there are other landslide
processes that go on up along the bluffs,

but this was a nice photo to show that,
yes, that is a substantial area of things

falling, but, again,
the lake continues to remove it.

And there are building setbacks
required, but it’s a special area,

but a small part of the bigger
Pennsylvania problem.

So next slide.

That’s the quickie tour
of most of the slides.

But I’ll whiz through here.
We’re running out of time.

But I want to talk about the impacts
of landslides in Pennsylvania.

Death and injury are blessedly rare.
Almost entirely related to highways –

rockfalls and somebody drives
into it, or a construction accident.

Something falls while a roadcut
is being wiped or something.

But we have lots of
damage to highways.

Lots of transportation
delays and detours.

Which can be pretty expensive.
And the societal impacts,

if a road is closed for any
substantial time, emergency access,

long detours,
school bus access.

And then repair costs,
obviously, are a factor there too.

We have, especially in urban areas –
which largely means Pittsburgh and

suburban damage to homes and
other buildings and loss of use.

Other infrastructure you don’t always
think about, but water lines,

sewer lines, gas lines, and electric lines.
Two of the fatalities I know of

in Pennsylvania were when a landslide
in a residential setting ruptured a gas

line, and the basement filled up with
gas, and the pilot light popped it off.

So that’s not real common but
is a significant [inaudible].

And then pipelines and railroads,
importantly, carry freight,

and increasingly, fuels.
Those locally produced –

Pennsylvania is a coal- and
an oil- and gas-producing state.

And we’re also seeing interstate
transport of things like Bakken

crude oil from North Dakota moving
through Pennsylvania on rail lines.

So I worry about both
of those in landslide areas.

Next slide.

And, again, this is supposed to be
a group of – sailing in, and it won’t,

probably, in your version.
If it does, you can click through.

On the left is a photograph of
the Buckeye Pipeline landslide.

The orange stripe up at the top is a
snow fence – an orange snow fence

indicating the location
of a former haul road

for a little coal mine
that was around the corner.

The coal was mined out,
and they abandoned the mine

and stopped maintaining the road,
which was just a dirt road.

It happens that this haul road was built
across a major petroleum pipeline.

And it was built up and probably
built correctly and so forth, but,

when the maintenance stopped, the
drains under the road got plugged up.

And, in a rainstorm in 1990, we got
the slide on the right – I don’t know

if that’s clicking through for you,
Matt, but – yeah, there are –

you got people standing
on top of a head scarp.

- We got it.
- And – yep, the landslide was

a fairly insignificant debris flow
until it ruptured a 10-inch,

quarter-inch-diameter pipe full of
transmix petroleum being sent

to a mixing station in Pittsburgh.
And this was a small valley –

filled up – I don’t know if you’ve got
the mashed pipe in your picture too.

Anyhow, 75,000 gallons of transmix
got dumped into this little tributary

valley to the Allegheny River well
upstream of Pittsburgh, but a number

of municipalities got their water from
the river and had to shut down.

And the National Guard had to
deliver water, and they closed areas

for, you know, gas fumes.
And the pipeline company was not

happy because they couldn’t rebuild,
and we wouldn’t let them run the pipe

around the head of the valley through
a number of other old landslides,

and they were shut down for quite a
long time and lost a lot of economic –

this used to be the most
expensive single landslide

I knew of in Pennsylvania, just
because of the damage and so forth.

Next slide.

You’ve heard of the Marcellus natural
gas play and – or the Utica play.

And Jaime knows more than
she wants to about this, perhaps.

In 2004, they started drilling new gas
wells for this wonderful new prospect

where they could kick over and drill
horizontally and hydrofrack through

some fairly thin black shales and
introduce lots of natural gas.

Well, here’s the – showing the
highly promising areas of this.

And you might notice that these
are somewhere close to some of my

highly susceptible landslide areas.
So we’ve got major oil and gas drilling

activity, gas wells, big platforms.
The big platforms are all up

on top of the hill, and they’re solid.
They’re not going anywhere.

But they need roads.
And they need pipelines.

And I am considerably worried
about the effects of those

in landslide-prone areas. And, in fact,
we’ve been getting lots of phone calls

for landslide maps from pipeline
companies and so forth.

But I do know we’ve had several
cases I’ve heard of in West Virginia,

but at least one case in Pennsylvania
in the last couple of years,

a small landslide ruptured
a gas-collecting pipeline,

or gas distribution –
I’m not sure which – pipeline.

The resulting explosion
destroyed a house.

Fortunately there were no people at
home, but a couple of horses and dogs

were killed. The people would
have been had they been home.

So this one is something that gives
me great concern about drilling activity

and pipeline and road construction
into previously pretty undeveloped

rural areas. And I worry
about this one a fair bit.

So [inaudible] Pittsburgh
backyard landslides.

At least partly human caused.
Here’s an example from the 1970s.

These are – happen anywhere
you have landslide country.

They’re not shock to any of you folks.
But we’ve had them in the 1970s.

We had another one in the 1990s.
This one, again, should have some

pictures sailing in, but I don’t know
that they will in your version.

The two houses at the top
were ultimately taken down.

The eight-unit apartment building
at the bottom was destroyed.

The apartment building at the left
was evacuated but later rehabilitated.

But the scarp was in the –
right at the foundation of this

upper house in the middle.
And trees from the landslide

poked through the siding
of the apartment complex.

And while it’s a fairly small landslide,
but when you’ve got houses in

the middle, it becomes an issue.
Next slide.

Again, I don’t know whether you can
do a series of click-ins on this or not.

But this is a similar backyard landslide
in a new and upscale housing

development south of Pittsburgh
in Washington County.

These were $300,000 homes
in a development that probably

had 100 houses.
And two roads in, and the toe

of this landslide blocked one of the
roads into the housing development.

And the shoulder of the landslide
was beginning to encroach

on the other road into
the housing development.

And ultimately, they had to move
the slide mass to open the lower road,

which meant that they didn’t dare
do this until the three houses

at the top were taken down
and – the houses falling.

So three people lost, you know,
three-year-old, $300,000 houses.

Now, to Californians,
that’s not a high real estate value,

but in Pittsburgh, those
are pretty nice houses.

So substantial damage effect there.
Next slide.

And this is the Kilbuck landslide.
Again, if you’re seeing the summary

view, it’s a little hard to trace the scarp,
but this was a former state hospital

grounds. Eventually
sold off for development.

Was going to have
a Walmart built on it.

They were regrading this slope in the
Pittsburgh red beds colluvium, and,

at 2:00 in the morning, it cut loose
and blocked four lanes of

a state highway that was a major
commuter route to Pittsburgh.

This is about five miles
west of downtown Pittsburgh.

And it blocked two lanes
of the Norfolk Southern Railroad’s

main line between
Chicago and the East Coast.

So, again, subsidiary damages.
It’s been sort of stabilized now.

But nothing will ever be built there,
and as far as I know, Walmart is

finding a hard time getting
anybody to take it off their hands.

There are lots of good stories to go
with it, but we’re running out of time.

Next slide.

So what good is our
technical knowledge?

We keep having landslides.

The state did, after the Walmart slide,
try to create a program

and wrote some legislation.
It never got out of committee.

We’ve heard
this story before.

Legal regulatory situation in
Pennsylvania is that there is no specific

authority, and the Pennsylvania
emergency management folks are

beginning to pay much more
attention to landslides,

partly after some events in 2018
that you’ll hear about next week.

But, again, mostly these are
small individual backyard slides.

They don’t rise to the level of disaster,
which floods do, and so it hasn’t

been on the emergency
management radar.

But all land use planning and
regulation in Pennsylvania is at

the municipal level. And there are
2,500 individual municipalities,

and some of them are very small
and don’t have much capacity.

Counties don’t have
much power here.

And next slide.
Hope for the future.

Some municipalities do have
good landslide zoning regulations.

We’re hoping more
will develop them.

Allegheny County has a new
landslide task force and a nice

web portal with information.
We’re hoping that will be productive.

Online maps seem to reach the public
better than the old paper maps.

They’re all used to looking at
Google Earth and using their GPSs.

And we’re looking forward
to the new federal legislation

and what that will bring.
And I think that’s it.