Why land sinks when we pump too much water

Pumping too much groundwater from underground aquifers causes the land above to sink, a process called subsidence. This happens when water, which fills spaces in soil and rock, is removed faster than it can be refilled, leading to compaction and collapse. In California's Central Valley, for instance, historical over-pumping for agriculture has caused the ground to sink by up to 9 meters in some areas since the early 20th century.