Gravity & Isostasy

Gravitational Force

• determined by mass and distance between objects

gravitational anomalies

differences in earth’s gravity field (measured vs actual)

GRACE satellites

• measure gravity field changes and detect water storage, ice melt, & tectonic activity

Isostasy

• gravitational balance between Earth’s crust and mantle buoyancy

Pratt Model

• difference in density determines topography

• high mountains = low density (floats higher)

• lowlands/valleys = high density (sink)

Airy Model

• difference in crust thickness determines topography (same density)

Mountain Erosion & Isostasy

• as mountains erode, crust rises to maintain equilibrium (isostatic rebound)

GIA

• glacial isostatic adjustment

• after glaciers melt, land rebounds upward

Isostatic compensation

• mountain building creates crust thickening triggering compensation (adjustment to return to equilibrium)

Archimedes Principle

• mass displaced = total mass

• Upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces.

• mass = density * volume

Mid Ocean Ridges (pratt model)

• heated lithosphere is less dense causing ridges to rise → create crust

Continental collision (airy model)

• thick crustal roots form under major mountain belts

Sea Level changes

• isostatic adjustments impact long term sea level rise and fall