May 30, 2021 02:33 AM
https://www.zmescience.com/science/geolo...s-sinking/
EXCERPT: . . . Subsidence is the geological process of ground sinking with no horizontal motion. It can happen quickly or slowly, and be natural or caused by human activity. It can be caused by things like mining or water extraction, or by voids or earthquakes. In Mexico City, subsidence is happening at a rate of 50 centimeters (20 inches) per year — and it’s not stopping.
It’s a pretty crazy rate, a city sinking by a person’s height every 3-4 years, but according to a new study led by Estelle Chaussard, a geoscientist at the University of Oregon, that’s exactly what’s happening. The researchers combined 24 years of space-based measurements and 115 years to show that large parts of the city are compacting at a steady rate.
[...] Subsidence in Mexico City doesn’t seem to reflect groundwater pumping rate. Instead, it seems to reflect the steady compacting of the ancient lake bed on which the city was built.
Mexico city was built on what was once Lake Texcoco, home of the Aztec city Tenochtitlán. Water usage in the area drove groundwater deeper and deeper, until the salty and clay-rich lake bed became dry. This lack of water left the loose mineral grains on the surface with a lot of room to compact — and that’s exactly what they’re doing. The rocks on the former lakebed are slowly compacting against each other, clumping together more tightly and causing subsidence.
[...] For Mexico City, this raises a host of long-term problems. Subsidence isn’t uniform in all parts of the city, so it can cause severe displacements or even fractures, damaging buildings and roads, as well as sewers and gas lines — potentially opening the way for contaminated water and maybe even worse issues... (MORE - details)
EXCERPT: . . . Subsidence is the geological process of ground sinking with no horizontal motion. It can happen quickly or slowly, and be natural or caused by human activity. It can be caused by things like mining or water extraction, or by voids or earthquakes. In Mexico City, subsidence is happening at a rate of 50 centimeters (20 inches) per year — and it’s not stopping.
It’s a pretty crazy rate, a city sinking by a person’s height every 3-4 years, but according to a new study led by Estelle Chaussard, a geoscientist at the University of Oregon, that’s exactly what’s happening. The researchers combined 24 years of space-based measurements and 115 years to show that large parts of the city are compacting at a steady rate.
[...] Subsidence in Mexico City doesn’t seem to reflect groundwater pumping rate. Instead, it seems to reflect the steady compacting of the ancient lake bed on which the city was built.
Mexico city was built on what was once Lake Texcoco, home of the Aztec city Tenochtitlán. Water usage in the area drove groundwater deeper and deeper, until the salty and clay-rich lake bed became dry. This lack of water left the loose mineral grains on the surface with a lot of room to compact — and that’s exactly what they’re doing. The rocks on the former lakebed are slowly compacting against each other, clumping together more tightly and causing subsidence.
[...] For Mexico City, this raises a host of long-term problems. Subsidence isn’t uniform in all parts of the city, so it can cause severe displacements or even fractures, damaging buildings and roads, as well as sewers and gas lines — potentially opening the way for contaminated water and maybe even worse issues... (MORE - details)