Sink Holes
19 messages in this thread
I'm about to make an offer on a house in Nortrhen New Jersey (Morris Township).
The area is not supposed to be known for sink holes, but that is exactly what
seems to have appeared on the front lawn.
The surface is a circular hole 8 to 10 inches in diameter. Unforunately I
didn't take the time for a careful examination, but it appeared to be a fissure
4 feet deep a foot wide and an undetermined lenght running off to one side. On
the surface in the direction of the fissure are several other small depressions
which felt solid when I bounced on them. About twelve feet away is a distinct
impression about 3 feet square (with fairly sharp edges).
The region itself is quite hilly, and the house is built half way up a moderate
slope that runs a 1/4 to 1/2 mile in total.
Any thoughts on what this might be, and what it would take to rectify the
condition would be greatly appreciated (the hole was certainly big enough to
swallow up my two year old).
TIA,
Andy
The last part of the previous message was apparently lost in transmission. The
reason for the posting is because I am seeking opinons of what might have
caused the hole, and what it would take to rectify the condition. The hole was
certainly big enough to swallow up my two year old.
TIA
Andy
Andy, Based on my similar experiences I would say you should gain some
information concerning if and when the property was filled in. My lot was
filled with trash that included logs of the trees that were standing on the
property. Thirty years later small pits ranging from inches to feet in size
and depth have appeared in several locations. When I dug down to investigate I
found the rotting wood. Generally filling the holes gives satisfactory
results, but the need for more fill dirt at irregular intervals is a pain, and
there is always the possibility that one of these mini-sinkholes will cause
someone some grief someday. -db-…
An obvious thought is a recently installed septic system, water line, utility
underground or other excavation subsiding or compacting.
based on a past experience, there could be an underground structure that has
rotted away. My brother and sister "disappeared" into a suddenly opening chasm
in the yard of an old farmhouse we lived in. The lawn had grown over very
rotten boards covering a (luckily) filled in well.
Regards- (and best wishes )
Michael
In addition to the relatively innocous explanations others have offered, there
is also a possibility that some amount of that gentle hillside is getting ready
to slide off in the direction dictated by gravity. I've forgotten the
technical term — something involving "slumping" I think. I think it's
uncommon, but it's not unheard of. Back in the 1950s that happened to a whole
housing development in Southern California. One may not want to buy the
property if it getting ready to move elsewhere.
Good point. Slump is the proper technical term, I think.
Michael: Do you have a hill?
– Greg Laden, Written 14-Oct-1994 @ 10:18:31
Using: Windows NavCIS PRO 1.25
Hi, Andy–
Welcome to the forum!
Michael has offered you some alternatives to sinkholes. Northern NJ is riddled
with a formation called the Franklin marble, which is dear to us fluorescent
mineral collectors. While I associate sinkholes with limestone, I suspect a
marble is equally vulnerable to dissolution by water, and may be prone to
sinkholes.
Can you tell us anything about the exposed rock in the hole? Is it smoothed by
water wear? That may provide a key for one of the pro geologists who visit
here (I am strictly an amateur in this field).
–Doug
>> Can you tell us anything about the exposed rock in the hole? Is it
>> smoothed by water wear? That may provide a key for one of the pro
>> geologists who visit here (I am strictly an amateur in this field).
I didn't notice any exposed rock, only soil.
Andy: The way you have described the occurence of the "sinkholes" and
associated depressions in a linear pattern is a classic example of dissolution
of a carbonate along an solutionally enlarged joint/fracture. I am not
familiar with the geology in this area and do not know if there is a rock unit
or Formation present that is suceptable to the process of dissolution. I
would suggest contacting a representative of the state geologist's office who
would perhaps have some information about the statistical occuence of sinkholes
in your area.
If it is a sinkhole occuring along a joint there are a few things that you can
do to "stabilize"( everything is relative) it. One thing not to do is dump
concrete into the hole or try to seal it off. What will happen if a vertical
soil pipe is plugged, is that the erosion will be displaced to some other point
along the joint and continue. If your house is located at that point …. A
method that has worked in the past in the Bowling Green, KY area is as follows.
Use a backhoe to remove the soil overlying the solutionally enlarged joint
until you have the bedrock on both sides exposed. Place rock, boulders, etc.
large enough to bride the gap in the excavation initially.
On top of these place a smaller size stone layer with a smaller stone size on
top of it until you arrive at approximatelly 0.5 in. below the surface. At
this point you can use a tight clay cap and top soil. What this does is to
allow the water level to fluctuate seasonally within the added rock without
soil erosion. In a sence you are working with the water instead of trying to
construct a barrier to it. Again, this situation could be the result of some
man-made structure and not associated with dissolution of a carbonate. Your
best bet ,IMHO, would be to contact someone with local geologic knowledge.
Good-Luck
Victor
Doug, Isn't marble just limestone subjected to pressure and heat? So unless
there's much chemical change, it should be dissolved by the same acidity that
dissolves limestone in Karst terrain. ? Anne
>> Doug, Isn't marble just limestone subjected to pressure and heat? So
unless there's much chemical change, it should be dissolved by the same acidity
that dissolves limestone in Karst terrain. ? Anne <<
Marble is way more resistant to chemical weathering than limestone.
GTL
– Greg Laden, Written 16-Oct-1994 @ 15:24:25
Using: Windows NavCIS PRO 1.25
Hi, Greg–
I reasoned like Anne, that marble would be subject to dissolution like
limestone, but hedged my bet because I had seen nothing to confirm this.
They are both CaCO3, mostly, so I figure any difference in weatherability is
likely mechanical. Perhaps marble is large interlocking crystals while
limestone is small grains cemented loosely together by more calcite, so
dissolving the cement would free the grains to roll away with the water?
–Doug
Sounds like a good explanation. All I'm sure of is that if you put acid on
limestone, you can see and hear the fizz very clearly, but if you put acid on
your marble coffee table, you can still get a fizz but it is a lot less
specacular!
Of course, this is all moot. With enough time, I suppose either could
dissolve enough to make caverins
On the other hand, I can't think off hand of any marble karstic terrains! Can
you? All the examples I can think of are limestone. Probably are marble
karstic terrains, and I just don't know about them..
Cheers,
GTL
– Greg Laden, Written 16-Oct-1994 @ 19:04:25
Using: Windows NavCIS PRO 1.25
<< All I'm sure of is that if you put acid on limestone, you can see and hear
the fizz very clearly, but if you put acid on your marble coffee table, you can
still get a fizz but it is a lot less specacular! >>
Although the reaction of your party host is much more spectacular when you put
the acid on the marble coffee table.
>> Although the reaction of your party host is much more spectacular when you
put the acid on the marble coffee table. <<
I was gonna say that but I couldn't find the words!
GTL
I want to thank everyone for the information, suggestions and well wishes.
Unfortunately for us it's all moot now, someone else out bid us on the house.
Thanks again,
Andy
Greg, Well, that's why geology wasn't my minor – I'm not good at chemistry!
Anne
Others have given good info to you, but I'd like to suggest a second
possibility. If you have a 4 foot deep hole and don't see any rock, then you
must have a lot of sediment on top. If this is a dissolution cavety in the
country rock, then you might have a hard time finding it by digging, because
the surface feature may not be as well correlated to the feature in the rock as
one might like, owing to water movement in the sediment.
If the sediment you see down in this hole is very sandy, you might just have
some kind of wierd groundwater feature. This happens on occassion in very
sandy areas. I've seen it (drove a car into one, in fact) on Cape Cod in very
sandy sediment. This probably means that it is not as serious as a sink hole,
in that a very large sink hole is a VERY LARGE sink hole!, while a groundwater
feature in sandy substrate is probably not going to get real big.
If you have easy access to a pile of fill, you may just throw it into the hole
and see if the problem goes away over the course of the coming winter and
spring. Also, you can get a long metal spike-like device, either a probe like
the kind that bottle diggers (damn them, BTW) use, or even a piece of
reinforcing rod. This may help determine if the low-spots you've got are
hollow underneath. Jumping up and down on them (perhaps a questionable
practice!) may not tell you enough.
As suggested, you should be very careful about the possibility that you've got
an old septic system in place. I assume that either your house is hooked up to
sewer, or that if it has a septic system, you know where it is and can rule
that out. But perhaps one existed previously. It should be located in a
"logical" place such as "downstream" from your sewer outlet. You may check
around in the basement or below your house for old sewer pipes heading in that
direction.
The highly linear shape of this features strongly suggests to me that it is
either a septic system or a trench (for a pipe) that was filled improperly,
either with bad fill or without tamping. For this reason, you should be
careful about probing (don't use a sledge on the probing bar or spike, for
example) so you don't go through any pipes.
You might try this: If you have natural gas going into your house, and this
feature is anywhere near where you can reasonably suspect that the gas line is
layed, call the gas company and ask them to have a look at it. Similarly,
public water/sewer or possibly electric company, if your electric lines are
underground, may be called. It could be a trench coming off one of their
lines, or even one of their lines going through your property.
On the same note, if you have an easment map or plat map of your property,
check for easments for such lines running across your land, and see if they
line up.
Good luck. Let us all know what happens!
Cheers,
GTL
– Greg Laden, Written 13-Oct-1994 @ 19:52:26
Using: Windows NavCIS PRO 1.25
Andy, Does that area have an underlying limestone formation? That's usual
where you get true sinkholes. Another thing to check would be if city sewers
or water mains run under the property – if there is a leak, you can get
underground washouts that look like sinkholes. Another possibility is an old
well – like that kid in Texas fell into a few years back. We have an old well
on our farm we had filled in which opened back up gradually, starting at a
surface hole about 8-10" across, and is now about 6 feet across. The area
underground is about 6-8' wide (and was that large even before the surface
caved in completely.
I came from Central Florida in an area well known for sinkholes, and
yours sounds small for a true one. BUT they can be small! There is no reliable
way to eliminate the possibility of there being underground caverns that could
collapse into real sinkholes. My father is a mining engineer who, during an
active period of sinkholes in central Florida, was drilling to prospect for
phosphate. He had a number of people contact him about drilling prospective
home sites to eliminate the possibility, but turned them all down. At that
time, in one subdivision, two and a half houses were sucked into a large
sinkhole, and people were very concerned.
I'd check with your city and on old maps for wells, water and sewer
lines. Anne