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The withdrawal of oil, gas, and groundwater are also blamed for the submerging delta. (Similar subsidence has been noted in Southern California and in many other states due to extensive pumping of groundwater, petroleum products and other reasons.)
Weight, drainage, industry
Geologists generally point to three major contributors to what has become the fastest-sinking land in North America.
The sheer weight of delta deposits constantly pushes downward, compressing all those moist, loose soils against the solid base below. In healthy deltas, new soils usually arrive fast enough to outpace the rate of compression. But when levees cut off the supply of new sediment on the Mississippi delta, compression gained the upper hand.
Drainage projects also speed subsidence, because removing water from moist delta soils causes them to compact. At the same time, draining exposes highly organic soils -- such as those composed of old marshes and swamps -- to decomposition, which can remove inches and even feet of elevation from some areas in a matter of decades. That's why communities developed behind protective levees have a lower elevation than the wetlands on the other side.
"Look at any of the (elevation) mapping we've done, and you'll see every community is lower than the wetlands they are being protected from," Dokka said. "And, in general, that is only going to get worse, especially as sea levels rise."
And while subsidence occurs naturally, industry activity can accelerate the process. Extraction of mineral deposits from beneath the delta has also been linked to subsidence by state and federal studies. Removal of oil and gas can create empty spaces beneath the surface, allowing layers above to collapse into the holes, adding to the subsidence. New laws require companies to fill these empty holes.
But the causes of subsidence are not restricted to the delta layers. Slippage along the web of fault lines in the Pleistocene layer below the southern half of the state has also been linked to dramatic increases in subsidence rates in specific locations, Dokka said.
originally posted by: seasonal
a reply to: waftist
I don't gripe about snow in Michigan, don't cry about the swamp you live in in Louisiana.
originally posted by: schuyler
Look, New Orleans should never have been built. These guys keep building in vulnerable areas and then claim. "Woe is me!" when no sensible people would have built in those areas anyway. Build on a flood plain and be surprised? Really? It's like building shoddy condos on the Florida coast. Hurricane? Who would have thought? The only disaster is the idiots who insisted on building there.