The Waters Increased Greatly upon the Earth
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11 responses to “The Waters Increased Greatly upon the Earth”
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Of course quite recently (5000 yrs ago) glaciers bumped Va. Beach region up a notch (in elevation), and now it is going back down a notch. So not too much debate about the problem, only debate is who pays and when, and what a correct permit process would look like. And maybe how much water rise to design for.
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The glaciers did not reach that far south. If they had, they would not have bumped the land up, but, rather, down. When glaciers retreat, the plate upon which they rested rises.
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Dick you *might* be correct about climate change, but I am quite sure the glaciers bumped your real estate up a good notch higher, and you are now sinking. You are correct that the glaciers pushed the land down, and the areas like Virginia that were not under the glaciers, got pushed up.
That’s the Virginia Big Blue argument, that because Virginia is already sinking, fossil fuels must be banned urgently or else Virginia will be lost to sea faster than we already are sinking.
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There is flooding you might be able to blame on storm surges fed by a rising sea level, and flooding caused by building in flat lowlands and cutting corners on the necessary drainage infrastructure, to save money and squeeze in a few extra building lots. Two different problems. I’d say that subdivision is mainly an example of the second.
Anybody building a permanent home in that Pungo area needs to understand that a Class 4 or 5 hurricane will come, will do what it will do, and their house will be damaged. You live near the ocean, you cast your dice. There is a reason why until 375 years after Jamestown that lovely land was still…..vacant. Duh. Great farm land, lousy for subdivisions. The green line? Wasn’t that what they called it? Made sense.
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If sea levels are rising and/or ground is sinking, no more development should occur in the flood plains. Maybe common sense instead of the state religion – developer worship – is occurring now and then.
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Hampton Roads is a poor petri dish for examining the effects of climate change and rising sea levels. Subsidence is often a more powerful force, especially over the short term. That certainly doesn’t make climate change a false prophesy and it doesn’t change the fact that building in flood prone areas is ill advised. It just makes places like Virginia Beach poor examples of the impact of sea level rising.
Drainage systems in flood prone areas are just another example of an externality of development. Road capacity, fire and police, schools and prisons and jails are other externalities. If all of the externalities were priced in a new home would need to pay a sky high proffer in order to pay for these externalities. But that would make the development community unhappy and the development community is where Virginia politicians go to stuff their pockets with donations. So, average citizens should expect to continue to subsidize inadequate proffers from new development until Virginians rise up and vote the current class of money grabbing politicians out of office.
Virginia needs campaign donation limits and vastly stricter rules regarding the disclosure of campaign donation expenditures. Until that happens the scams will continue.
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Dick, the glaciers (Laurentide ice sheet) caused a forebulge here, pushing the land upward –like a throw rug that’s pushed from one end and rises in the middle. As the glaciers withdrew starting 18,000 years ago, so did the pressure causing the bulge (glacial isostatic adjustment). The subsidence from that is about 1 mm a year. (page 14, USGS Circular 1392 Land Subsidence and Relative Sea-Level Rise in the Chesapeake Bay Region. https://pubs.usgs.gov/circ/1392/ )
Page 17: “Aquifer system compaction estimated to be 1.5 to 3.7mm/yr can explain the majority of observed land subsidence.”
So half or more of the relative sea level rise is from subsidence, not global SLR.
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Thank you for the info. Do we have a feel for how many total feet the glaciers pushed our shoreline up? And presumably that would be how many total feet the land could go down in the long term?
Groundwater as separate effect I presume…I assume the groundwater compaction is due to groundwater extraction for drinking/industry? I knew about the groundwater impact on subsidence, but I did not mention it above.
@Steve the other problem with Jamestown was water supply as they had a severe drought in that era. If we had a similar drought today, can you possibly imagine?
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“Geological Change and Flooded Valleys
The Choptank River is the largest tributary of the Chesapeake Bay on the eastern shore and is therefore part of the largest estuary in North America. This Bay and all its tributaries were once non-tidal fresh water rivers and streams during the last ice age (15,000 years ago) when sea level was over 300 feet below present. As climate warmed and glaciers melted northward sea level rose, and the Choptank valley and Susquehanna valley became flooded. Such flooded valleys are called estuaries where ocean salt water mix with fresh river water producing some of most biologically rich waters in the world. Thus the Chesapeake has been called an “immense protein factory.” See:
http://choptankriverheritage.org/Documents/Lower%20Choptank%20Inventory.pdf
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Thanks. I have long been interested in Virginia geology and, now that I have the time, I intend to educate myself even more.
By the way, I did note in my post that sea level rise in Virginia Beach was only partially attributable to climate change.
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Reed,
One glitch in the Choptank River piece. The Chesapeake Bay was created by the bolide impact when the crater filled with sea water. Fresh water did flow into it from the river systems, but it started out as very salty. (The trapped pockets of ancient sea water in Mathews confirm that!)Something you don’t see mentioned very often: “Sea level was unusually high everywhere on Earth, and the ancient shoreline of the Virginia region was somewhere in the vicinity of where Richmond is today (fig. 1).” (USGS Fact Sheet 049-98, https://pubs.usgs.gov/fs/fs49-98/ )
TBill:
I’ve never seen a number given on total impact of isostatic changes. I’m not sure there’s any way to tell since the crust floats on magma. From what I read in one paper, the density of the material in the crust and the amount of glaciation determined the point where equilibrium was established. But given the changes in the land mass over the past 18,000 years, how could the change in density be calculated?It’s the compaction of the aquifer, not ground water itself. When too much groundwater is removed for drinking or paper mill processing, the spaces between sand and stone fill in with silt, so water no longer holds that space open. There’s no way to reestablish those spaces once compacted.
There’s one statement about subsidence that’s been changed over the years: if we were still experiencing subsidence from the impact, after 35 million years, even at 1 mm a year, that would mean dropping 21 miles. That didn’t happen. The crater settled down a long time ago and filled in with sediment too over the ages to where it is today. I don’t know the stats for Virginia Beach, but Mathews is completely inside the crater, and wetlands are able to add sediment and maintain pace with sea level rise of up to 7.5 mm a year — if erosion doesn’t eat away the shoreline. (EPA 430R07004, Coastal Sensitivity to Sea Level Rise, Titus and Strange, 2008.)
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