VOLUMETRIC STRAIN
20–100 cm
water-level rise
(0.5–3 feet)
SHEAR STRAIN
Undisturbed
water level
1 microstrain
contraction
Contraction -> water level up
Expansion -> water level down
No detectable
water-level
change
1 microstrain
shear strain
Shear or distortion with no
volumetric change ->
no water level change
VOLCANO DEFORMATION–Geodetic Monitoring Techniques
By Daniel Dzurisin
U.S. Geological Survey graphics