Florida Sinkhole Highlights State's Geologic Instability

An anonymous reader writes "Last Thursday night, a sinkhole took the life of a man (TV news video, with ad) while he slept in his home in Seffner FL, near Tampa. While human fatalies are rare, sinkholes are so common in Florida that the insurance industry successfully lobbied the state lawmakers to pass legislation in 2011 making it more difficult for homeowners to claim sinkhole damages. The bedrock in Florida is limestone, a weakly soluble mineral formed from calcified deposits of sea creatures tens of millions of years ago. Above the limestone is a clay layer called the Hawthorn Formation which shields the limestone from ground water; and above the clay is sand. However, the protective clay layer is thin or nonexistent in some areas of Florida, particularly in the middle part of the state near the Gulf coast, where caves and sinkholes are common. Geologists say that human activity, particularly construction and irrigation, can trigger sinkholes by destabilizing the landscape above caverns by drawing down water tables and massing structures above them."

Comments

Who would have thought

[ArchieBunker]

it was a great idea to start building homes on swamp land?

Re:Who would have thought

[Frosty Piss]

...it was a great idea to start building homes on swamp land?

They have to build them someplace. Where would you suggest?

Re:Who would have thought

[Trepidity]

There's a lot of empty space in Montana I hear.

Re:Who would have thought

[K. S. Kyosuke]

it was a great idea to start building homes on swamp land?

If the castle sinks, you build another one on top of it. Repeat until it stands. (Then, marry a princess with huge...tracts of land.)

Re:Who would have thought

[Mashiki]

it was a great idea to start building homes on swamp land?

This doesn't have anything to do with swampland really, rather it has to with the limestone that makes up the base of Florida. Same with really anywhere there's limestone, Ontario, Michigan, parts of Quebec, large swaths of the NE US. Some places are more stable than others and don't have to worry about it. And there's no much you can do in some cases, and while the limestone is thick where I live several hundred feet there have been huge sink holes.

Re:Who would have thought

[YrWrstNtmr]

Texas

Hurricanes.

Re:Who would have thought

[hairyfeet]

Arkansas? Pretty countryside and the majority of it is on solid bedrock. Pretty rivers, pretty mountains, lots of pretty nature and prices are a hell of a lot cheaper than in FL which is probably why we are suddenly getting so many retirees here.

But sometimes you just need to cut your losses which it sounds like there are parts of Florida that just aren't any good for building, same as i never understand why they keep rebuilding New Orleans, the whole reason it was put where it was was on account of river trade which isn't a big money maker anymore and its below sea level folks, time to accept that NO is a swamp and let it go, build farther up and a little higher off the ground and call that NO and be done with it. If that area of FL is so littered with sinkholes you are at risk of your house disappearing any minute time to pack up and move folks, just not a smart place to be.

Re:Who would have thought

[Yobgod Ababua]

Come on... please quote properly for full comedic effect.
"
When I first came here, this was all swamp.
Everyone said I was daft to build a castle on a swamp, but I built in all the same, just to show them.
It sank into the swamp.
So I built a second one.
That sank into the swamp.
So I built a third.
That burned down, fell over, then sank into the swamp.
But the fourth one stayed up.
And that's what you're going to get, Lad, the strongest castle in all of England.

Re:Who would have thought

[c0lo]

Texas.

For the frying pan into the fire: sinkholes too.

Re:Who would have thought

[girlintraining]

If the castle sinks, you build another one on top of it. Repeat until it stands. (Then, marry a princess with huge...tracts of land.)

Move to Minnesota. It's the most geologically stable location on the planet. There's a reason it's called the Iron Range. We have no earthquakes, hurricanes, and our buildings don't mysteriously vanish into holes in the ground. We have access to the largest reservoir of fresh water in the world as well. Global warming? Not a problem up here. Fertile farmland? Got that in spades too. Everything you need to survive just about any natural or man-made disaster is abundant here. We can survive the apocalypse. And we do, for three months out of the year, every year.

Our state budget has been balanced nearly every year. Ever. We have contributed far, far more to the federal government than we've gotten back. We're not number one in murders, shootings, rapes... or worst of all, politicians and lawyers. Every now and then one of the major parties gets the idea in their head of hosting their national convention up here. We make sure to kill 'em with nice, and they don't come back for a good long time after.

I gotta say, the things you people go through because you're afraid of a little snow is unbelieveable. Malaria. Hook worms. Giant mouths full of teeth attached to a hide thick enough to repel small arms fire (it's called an alligator). Your buildings are routinely eaten by nature, sometimes quite suddenly. Your summers are so scorching hot they're having to invent new colors to describe exactly how long you have to live once the air conditioning goes out. You don't have enough water, and fight with each other over it.

Be a little cold, or risk every other malady known to man. Apparently... it's a defect in our DNA. We'll tolerate anything as long as it doesn't make us shiver, or obstruct the free flow of traffic...

Re:Who would have thought

[SternisheFan]

...it was a great idea to start building homes on swamp land?

They have to build them someplace. Where would you suggest?

You can build in wetlands IF you drive LOTS of friction pilings for each structure deeply enough. You might need to replace soil, even put in a raft foundation to evenly distribute the home's weight.

"Raft foundation is a thick concrete slab reinforced with steel which covers the entire contact area of the structure like a thick floor. Sometimes area covered by raft may be greater than the contact area depending on the bearing capacity of the soil underneath. The reinforcing bars runs normal to each other in both top and bottom layers of steel reinforcement. Sometimes inverted main beams and secondary beams are used to carry column loads that require thicker foundation slab considering economy of the structure. Both beams cast monolithically with raft slab."

http://civil-engg-world.blogspot.com/2012/06/what-is-raft-foundation-difference.html?m=1

http://menbuy.net/home-improvement-2/preparations-for-building-in-a-swamp/

Re:Who would have thought

[rgmoore]

There's a reason it's called the Iron Range.

Yes. It's because there's lots of iron ore there. It has nothing to do with geological stability, though Minnesota is nicely stable. Of course that stability means that what passes for a mountain there is pretty laughable.

We have no earthquakes, hurricanes, and our buildings don't mysteriously vanish into holes in the ground.

Yes, but you do have floods, blizzards, and pestilential mosquitoes in the summer. Your winters are so miserable that people literally live in giant shopping malls so they don't have to go outside.

We have access to the largest reservoir of fresh water in the world as well.

No you don't. Both Lake Baikal and Lake Tanganyika are larger than Lake Superior by volume, which is the only sensible measure of how much fresh water a lake contains. Lake Baikal has a larger volume than all 5 great lakes combined.

Look, I'm sure that Minnesota is a nice place. It seemed nice when I visited. But it has its own set of problems, and it lacks things that other places have that people who live there really enjoy. I'm glad you like it there, but don't try to impose your ideas of what an ideal place looks like on everyone else.

Florida state website about it

[Trepidity]

The state's Department of Environmental Protection has a nice collection of sinkhole resources, including a database of incidents, and a poster with a map.

Re:What's The Tech Angle?

[Frosty Piss]

What's the tech angle to this story? It's a sinkhole. Ground cover collapse is not a Slashdot story.

Oh, I don't know.. Geology? Engineering? Perhaps involving technology to detect and prevent these things?

Something like this perhaps?

Aquafilter pumping

[jacobsm]

Let's pump massive amounts of water out of the aquafilter. What could possibility go wrong? (Living in West Central Florida on the edge of a well field).

Re:Aquafilter pumping

[Grayhand]

Aquifer. I don't think this is connected to groundwater pumping.

It can be the start of a sink hole. Drawing out too much water can make the aquifer collapse. It can create a void where rain water flows into washing away the collapsed parts of the aquifer creating an actual void. With broken water lines they can form in days or weeks this one could have taken years. What's scary is they used to be rare events but they are getting more common so something has changed. Just building housing developments changes the flow of water with unknown effects. Most seem to happen along coastal areas, say 20 or 30 miles of the ocean so drained aquifers and redirected water would be the likely causes. look at it this way, aquifers have been stable for thousands of years then we remove billions of gallons from them in a few decades and don't expect a problem? Think of them as big water beds. What happens to your water bed when the water drains out? Now picture it with porous rock only you stick a hose in and start intermittently flushing water in and out. When there was water in the rock it would buffer the affect of the new water but now it flushes freely through the voids washing parts away. Parts of Florida are a ticking time bomb. Personally I think the bigger problem is brackish water flooding the aquifers. The aquifers are retreating at several feet a year so eventually the fresh water will all be miles inland. All those private wells will be pumping sea water.

Re:Aquafilter pumping

[Anonymous Coward]

This is it. Farmers are taking the water for their crops. Not to irrigate them, but to run water on the night after night to stave the frost. The net result is more and more property are sinking because the aquifers have lost most of their water.

Farmers and the counties need to work on using reclaimed water for frost prevention, and not steal the public water table at the costs of people losing their homes.

Re:Aquafilter pumping

[peragrin]

sounds like god is getting his chain saw out to cut florida out of the USA.

It is only old folks and cubans anyways there really isn't anything to be missed there.

Re:Pretty clever

[CncRobot]

The state runs the insurance company that most people in Florida have to use now, called Citizens. It wasn't a "problem" until the state had to start paying out, before when it was just private insurance companies this wasn't as big of an issue.

Re:Pretty clever

[Anonymous Coward]

Smart of the insurance industry to make themselves useless. Now, if they never fork out, why should I have an insurance?

Because the bank requires that you pay for insurance as part of the mortgage.

Because the state requires that you pay for insurance to drive legally.

The insurances companies have been tremendously smart. Securing mandates that you pay more and more for their products, acquiring guarantees of profits, all while reducing their liability and payouts.

Tech Angle

[PPH]

Perhaps someone can come up with some seismic sensing technology that can detect underground voids. Similar to what the oil and gas people use, but optimized for shallower depths.

Communities could do a periodic survey in populated areas and give property owners some advanced notice to evacuate their property. The down side is that existing property owners won't want a pre-sale seismic survey to become common practice.

Re:Tech Angle

[Diamonddavej]

The technology for mapping subsurface voids has been around for decades, at least the 1960s, the most common method is Direct Current / Resistivity Surveying. An electric current is passed though the ground between four electrodes and the apparent resistivity (in Ohms/meter) of the subsurface is measured & mapped. Voids, filled water or clay or even empty space, have a completely different resistivity compared to the surrounding rock.

Modern survey instruments are automated, they use dozens of computer controlled electrodes (2 current and 2 voltage electrodes are active at any one time). On open ground, a survey covering an area football field could be carried out in a few days. Geophysicists were using Resistivity Surveying to map the sinkhole in Seffner, Florida.

However, I don't know if Florida state law quires a subsurface ground survey before homes are built, I wouldn't be surprised if lobbyists managed to keep such a law off the books (like the insurance lobbyists). Also, the home involved in this case might have been built before automated surveying became available in the 1990s, before then it was slower, more expensive, not widely used.

Engineers Conducing a Resistivity Survey"

2-DAND 3-D RESISTIVITY FOR LOCATING VOIDS BENEATH HIGHWAYS THREE CASE STUDIES"

Re:What's The Tech Angle?

[Ol Biscuitbarrel]

Some tech input will show up regardless of what's in TFS/A. General science articles are always welcome for me at any rate. Regarding this topic, here's a good photo gallery: Notable sinkholes from around the globe.

Re:An Acceptable Risk

[Trepidity]

Not to mention that, even in Florida itself, hurricanes are a much larger risk than sinkholes.

Pump in sand?

[Archeopteryx]

Perhaps if you could identify where this was happening, it could be remediated by pumping in a slurry containing solids that would lock in place and resist leaching like coal ash and some kinds of sand?

Any civil engineers care to comment on that?

Re:Pump in sand?

[evanbd]

Given the stuff in coal ash, I don't think I want it pumped into places in contact with groundwater that people drink.

Re:Pump in sand?

[evanbd]

Coal ash is the solid stuff left after you burn the coal. The carbon (and heavy hydrocarbons) in coal is the stuff that burns. The stuff left behind has very, very low carbon content. The carbon basically all comes out as CO2 gas.

Re:Pump in sand?

[riverat1]

No you can't. There isn't much carbon in coal ash. It's what's left over after they burn (nearly) all of the carbon out of coal.

Re:Pump in sand?

[hey!]

Well, the sinkhole in question is believed to be 100' across and 15' - 30' deep. That's about 4400 cubic yards of fill material, which is *not* lightweight. The material would be staged on or near unstable ground and the work would no doubt be hazardous. It'd be a complicated and dangerous engineering project; maybe if a sinkhole like this developed under Monticello, but we're talking about a couple of ramshackle ranch houses. It'd make more economic sense to put up a fence and let them fall into the ground.

Re:Pretty clever

[arashi no garou]

Because the state requires that you pay for insurance to drive legally.

Only if you don't have the money to cover the minimum liability. If you do have money, as long as it is set aside in one of couple ways so it can't disappear before needed, you don't need insurance to drive.

Are you speaking just of Florida? Because it's different in every state. Here in Georgia you have to have liability coverage at minimum to legally operate a vehicle, even if you have thousands in a savings account named "just in case I'm a bad driver". There was a time when you didn't have to have insurance in Alabama, but a few years ago they mandated minimum liability insurance coverage as well.

I'm normally not keen on the government telling us how to live our lives, but having mandatory liability coverage is a no-brainer for the vast majority of poor and middle-class citizens who simply can't be assumed to be responsible enough to have a personal insurance savings plan, and can't afford a huge payout if they do cause an accident. I'd rather pay $50/month to insure that I won't be sued and bankrupted because I made a mistake driving, than bank that money and hope that I've saved up enough to fight said lawsuit.

On the other side of the coin, I'd much rather the person who hits me has liability coverage, so their insurance company takes care of me instead of leaving me to chase after their assets in court. Also, I wouldn't be surprised if states without mandatory liability coverage have more hit-and-run accidents than other states.

California vs Florida

[Freddybear]

When I lived in Miami we used to say that California might slide into the Pacific Ocean but Florida would disappear into it's own asshole.

Yeah, it figures.

[mark_reh]

Insurance companies might have to pay some money out, so they buy the state legislature to write laws allowing them to screw the insurance purchaser.

How long will insurance companies keep getting their way? They did the same with health care. If someone is sick they don't want to insure them because they might have to actually pay out some money. The insurance industry is more evil than cell phone and cable TV companies combined.

We are stupid and deserve the government we elect. The human race is doomed to extinction before we figure out how to get off this rock.

Re:Pretty clever

[MartinSchou]

I'm normally not keen on the government telling us how to live our lives, but having mandatory liability coverage is a no-brainer for the vast majority of poor and middle-class citizens who simply can't be assumed to be responsible enough to have a personal insurance savings plan, and can't afford a huge payout if they do cause an accident

Emphasis added.

First of all - fuck you.
Secondly - fuck you some more.

If you're poor, how the fuck are you supposed to put money aside for a personal insurance savings plan? Especially in the US, where people are likely to get sued for anything and the cost of any kind of medical assistance is likely to be ruinous if not for insurance.

Seriously - you even pointed it out yourself, right after you made your quite frankly extremely insulting comment!can't be assumed to be responsible

Montana

[fyngyrz]

There's a lot of empty space in Montana I hear.

Wait, what? No, no empty space here. Not any. You want Texas. It's not being used for much useful other than producing oil, cattle and ignorance (not quite certain which is the state's leading export, actually.) Get some real schools in there, teach science instead of superstition, invite immigrants to help out... you'd have an actual useful state before you knew it.

But not Montana. Please. Besides. I really don't think you'd like our -40 temps in the winter. Texas, on the other hand... perfect.