How pumping causes subsidence

When pumping causes declines in groundwater levels, clay layers may compress and cause the land above to sink.

Diagram shows how water drawn from an aquifer compresses sand and gravel, causing the land above it to sink

SIERRA

NEVADA

Sand and gravel

(permeable aquifer)

COAST

RANGES

Water table

Well

San Joaquin Valley

Recharge

Recharge

Groundwater

Clay or silt aquitards

Land

surface

Former land surface

Subsidence

Coarse

sand and

gravel

Fine clay

and silt

Fine-grained

aquitard is

compacted

when water is

extracted

Coarse

sand and

gravel

Diagram shows how water drawn from an aquifer compresses sand and gravel, causing the land above it to sink

SIERRA

NEVADA

Water

table

Sand and gravel

(permeable aquifer)

COAST

RANGES

Well

San Joaquin Valley

Recharge

Recharge

Groundwater

Clay or silt aquitards

Subsidence

Former land surface

Land

surface

Coarse

sand and

gravel

Fine clay

and silt

Fine-grained

aquitard is

compacted

when water

is extracted

Coarse

sand and

gravel

(Drawings not to scale; size of grains of sand, gravel, silt and clay are exaggerated.)

U.S. Geological Survey

Paul Duginski LOS ANGELES TIMES