By Hydrosimulatics INC  

Original content source (unless stated otherwise) :https://www.usgs.gov/special-topic/water-science-school/science/land-subsidence

Subsidence is a problem everywhere!

Subsidence is a global problem and, in the United States, more than 17,000 square miles in 45 States, an area roughly the size of New Hampshire and Vermont combined, have been directly affected by subsidence. More than 80 percent of the identified subsidence in the Nation has occurred because of exploitation of underground water , and the increasing development of land and water resources threatens to exacerbate existing land-subsidence problems and initiate new ones. In many areas of the arid Southwest, and in more humid areas underlain by soluble rocks such as limestone, gypsum, or salt, land subsidence is an often-overlooked environmental consequence of our land- and water-use practices.

When you look at the photo below of the Basilica in Mexico City, do you find yourself asking if it might not look straight? In fact, the foundation of the Basilica on the left is sinking and this sinking phenomenon is happening throughout Mexico City, where long-term extraction of groundwater has caused significant land subsidence and associated aquifer-system compaction, which has damaged colonial-era buildings, buckled highways, and disrupted water supply and waste-water drainage. Some buildings have been deemed unsafe and have been closed and many others have needed repair to keep them intact.

Land subsidence is most often caused by human activities, mainly from the removal of subsurface water. The photo at the bottom of this page shows a fissure near Lucerne Lake in San Bernardino County, Mojave Desert, California. The probable cause was declining groundwater levels. Here are some other things that can cause land subsidence: aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost.