Jan 20, 2021 07:40 PM
https://www.wired.com/story/the-ongoing-...-aquifers/
EXCERPT: As California’s economy skyrocketed during the 20th century, its land headed in the opposite direction. A booming agricultural industry in the state’s San Joaquin Valley, combined with punishing droughts, led to the over-extraction of water from aquifers. Like huge, empty water bottles, the aquifers crumpled, a phenomenon geologists call subsidence. By 1970, the land had sunk as much as 28 feet in the valley, with less-than-ideal consequences for the humans and infrastructure above the aquifers.
The San Joaquin Valley was geologically primed for collapse, but its plight is not unique. All over the world—from the Netherlands to Indonesia to Mexico City—geology is conspiring with climate change to sink the ground under humanity’s feet. More punishing droughts mean the increased draining of aquifers, and rising seas make sinking land all the more vulnerable to flooding. According to a recent study published in the journal Science, in the next two decades, 1.6 billion people could be affected by subsidence, with potential loses in the trillions of dollars.
“Subsidence has been neglected in a lot of ways because it is slow moving. You don't recognize it until you start seeing damage,” says Michelle Sneed, a land subsidence specialist at the U.S. Geological Survey and coauthor on the paper. “The land sinking itself is not a problem. But if you're on the coast, it's a big problem. If you have infrastructure that crosses long areas, it's a big problem. If you have deep wells, they're collapsing because of subsidence. That's a problem.”
For subsidence to become a problem, you need two things: The right kind of land, and an over-exploited aquifer. Aquifers hold water in between bits of sand, gravel, or clay. When the amount of clay in an aquifer is particularly high, the grains arrange themselves like plates thrown haphazardly in a sink—they’ve basically got random orientations, and the water fills in the spaces between the grains. But if you start extracting water from an aquifer, those spaces collapse and the grains draw closer together. “Those plates rearrange themselves into more like a stack of dinner plates that you put in your cupboard,” says Sneed. “It takes a lot less space, obviously, to stack the plates that way. And so that's the compaction of the aquifer system that then results in land subsidence at the surface.”
But wouldn’t pumping more water back into the aquifer force the clay plates back to their random, spacey orientations? Unfortunately, no. [...] gradual subsidence isn’t as destructive as a sudden earthquake or volcanic eruption. “But it will cause these indirect effects or impacts that, in the long term, can produce either damages to structures or infrastructure, or increase floodable areas in these river basins or coastal areas,” says geoscientist Gerardo Herrera-García of the Geological and Mining Institute of Spain, lead author on the paper. ... Humanity has tended to construct its cities where rivers empty into the sea, where the conditions for subsidence are ideal. ... Cities built on landfill are also sinking as that material settles...
Subsidence gets even trickier because its effects can vary dramatically over short distances, depending on factors like local clay composition [...] Really, the only way humanity will be able to stave off subsidence is to stop over-exploiting aquifers, a tall order on a rapidly warming planet. “Aquifers will be depleted, one way or another,” says Shirzaei. ... That could mean elevating buildings on lands that are subsiding and flooding. It could mean relying more on desalinating seawater, though that remains highly energy intensive ... Or cities might follow in the footsteps of Los Angeles, which is modifying its streets to collect precious rainwater.
At the end of the day, subsiding cities are up against unstoppable physical forces. “Geology is geology,” says Sneed. “We can't do anything about that.” (MORE - details)
EXCERPT: As California’s economy skyrocketed during the 20th century, its land headed in the opposite direction. A booming agricultural industry in the state’s San Joaquin Valley, combined with punishing droughts, led to the over-extraction of water from aquifers. Like huge, empty water bottles, the aquifers crumpled, a phenomenon geologists call subsidence. By 1970, the land had sunk as much as 28 feet in the valley, with less-than-ideal consequences for the humans and infrastructure above the aquifers.
The San Joaquin Valley was geologically primed for collapse, but its plight is not unique. All over the world—from the Netherlands to Indonesia to Mexico City—geology is conspiring with climate change to sink the ground under humanity’s feet. More punishing droughts mean the increased draining of aquifers, and rising seas make sinking land all the more vulnerable to flooding. According to a recent study published in the journal Science, in the next two decades, 1.6 billion people could be affected by subsidence, with potential loses in the trillions of dollars.
“Subsidence has been neglected in a lot of ways because it is slow moving. You don't recognize it until you start seeing damage,” says Michelle Sneed, a land subsidence specialist at the U.S. Geological Survey and coauthor on the paper. “The land sinking itself is not a problem. But if you're on the coast, it's a big problem. If you have infrastructure that crosses long areas, it's a big problem. If you have deep wells, they're collapsing because of subsidence. That's a problem.”
For subsidence to become a problem, you need two things: The right kind of land, and an over-exploited aquifer. Aquifers hold water in between bits of sand, gravel, or clay. When the amount of clay in an aquifer is particularly high, the grains arrange themselves like plates thrown haphazardly in a sink—they’ve basically got random orientations, and the water fills in the spaces between the grains. But if you start extracting water from an aquifer, those spaces collapse and the grains draw closer together. “Those plates rearrange themselves into more like a stack of dinner plates that you put in your cupboard,” says Sneed. “It takes a lot less space, obviously, to stack the plates that way. And so that's the compaction of the aquifer system that then results in land subsidence at the surface.”
But wouldn’t pumping more water back into the aquifer force the clay plates back to their random, spacey orientations? Unfortunately, no. [...] gradual subsidence isn’t as destructive as a sudden earthquake or volcanic eruption. “But it will cause these indirect effects or impacts that, in the long term, can produce either damages to structures or infrastructure, or increase floodable areas in these river basins or coastal areas,” says geoscientist Gerardo Herrera-García of the Geological and Mining Institute of Spain, lead author on the paper. ... Humanity has tended to construct its cities where rivers empty into the sea, where the conditions for subsidence are ideal. ... Cities built on landfill are also sinking as that material settles...
Subsidence gets even trickier because its effects can vary dramatically over short distances, depending on factors like local clay composition [...] Really, the only way humanity will be able to stave off subsidence is to stop over-exploiting aquifers, a tall order on a rapidly warming planet. “Aquifers will be depleted, one way or another,” says Shirzaei. ... That could mean elevating buildings on lands that are subsiding and flooding. It could mean relying more on desalinating seawater, though that remains highly energy intensive ... Or cities might follow in the footsteps of Los Angeles, which is modifying its streets to collect precious rainwater.
At the end of the day, subsiding cities are up against unstoppable physical forces. “Geology is geology,” says Sneed. “We can't do anything about that.” (MORE - details)