Investigation: Isostasy and Global Elevation Patterns

Investigation: Isostasy and Global Elevation Patterns • Student Learning Outcome : • Quantify relationships between mass, volume,and density • Calculate the density of basalt and granite samples from measurements of their mass and volume • Calculate the mean and standard deviation of density for granite and basalt sample populations • Generalize basalt and granite samples as representative of typical oceanic and continental crust • Visualize Archimedes’ principle that a floating object displaces a volume of liquid equal to the object’s mass • Explain the bimodal distribution of global elevations as result of isostatic equilibrium among oceanic and continental crust

Archimedes’ Principle:“A floating body will displace a volume of fluid whose massis equal to that of the body” Increase body density, body floats lower in fluid Increase fluid density, body floats higher in fluid

Archimedes’ Principle:“A floating body will displace a volume of fluid whose massis equal to that of the body” Increase in body height, body floats higher in fluid . . . but same percentage of icebergs’ heights (~10%) are above the water surface

Archimedes’ Principle:“A floating body will displace a volume of fluid whose massis equal to that of the body” Link to wooden block floating in water model . . .

Archimedes’ Principle:“A floating body will displace a volume of fluid whose massis equal to that of the body” Link to wooden block floating in water model . . . Think of oceanic crust as a thinner denser block“floating” lower on underlying asthenosphere than continental crust Oceanic Crust Column Continental Crust Column

Concept of Hypsographic Curve What variables are being presented?How are variables related?

Concept of Hypsographic Curve What variables are being presented?How are variables related? General Patterns? Responsible Processes?

Part A. Comparing Densities of Oceanic and Continental Crust

Let’s calculated the hydrostatic pressure at the base of the asthenosphere for the “Average Oceanic Crust” column:Assume column sides are 1 m by 1 m!Pressure = density*thickness*gravityFirst calculate pressure from seawater, then oceanic crust, then mantle.Sum the three pressures for thetotal pressure Part B. Testing the Isostasy Prediction

Go to Web-Based Isostasy Model Part C. Predicting Elevations at the “Tops” of Blocks ofContinental and Oceanic Crust

Mostly Continental or Oceanic? Mostly Continental or Oceanic? Part D. Connecting Global Elevation Patterns to Differencesin Oceanic and Continental Crust

Part E. Out of this World:Using isostatic principles to make Predictions for Mars

Investigation: Isostasy and Global Elevation Patterns