Isostasy Flashcards
What is hydrostatic isostasy?
Stress balance (gravitational equilibrium) in a vertical direction only. (Horizontal, shear stresses ignored. Each column of lithosphere considered in isolation).
What is the hydrostatic compensation depth, Zk?
In the hydrostatic model, Zk is the minimum depth below which no more density differences occur. Here, the weight of all columns is equal.
If using the surface of the earth as the reference level, what are movements relative to this called?
Burial (down) or exhumation (up)
If using the surface of an undeformed reference lithosphere (H), what are movements relative to this called?
Subsidence (down) or uplift (Up)
What is the difference between the Airy and Pratt hydrostatic isostasy models?
The Airy model considers all the blocks to be of the same density but difference thicknesses. The Pratt model assumes that all blocks have different densities but float at the same depth. Note: both models can only be applied locally.
What would you use the Airy or Pratt isostatic models?
The Airy model is handy for explaining continental settings and crustal roots. The Pratt model is better suited to near MOR settings as it is dependent on density changes.
What does the flexural isostasy model measure?
The flexural isostasy model explains how large topgraphic loads e.g. seamounts, can be compensated by regional lithospheric displacement through elasticity and lateral forces.
What are the isostatic effects of erosion and deposition?
Erosion reduces the load which causes the crust to rise. Deposition increases loading which causes subsidence again.
What is the curvature of the temperature depth gradient in the geotherm dependent on?
Amount of heat production and conductivity (K)
What is Poisson’s ratio?
Lat strain/long strain
What is the bending moment?
Integrated effect of the bending stress
When is hydrostatic isostasy invalid?
If the object is much thicker than wide.
