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MS 20 Introduction To Oceanography Isostasy Team Number: Team Leader: Team Members: Section Time: Record all data in the appropriate metric units (centimeters, grams, etc.). Remember to use significant figure rules and to indicate appropriate units (if the scale reads 13.4 g, your answer is not 13.4, but 13.4 g (or 13.4 grams). A. Demonstrating Archimedes’ Principle Pine Block Oak Block Mass of block <grams> Weight of water in pan <grams> Displaced volume <cm3 or mL> (volume of water in pan) Block thickness <cm> Length of side <cm> Vblock (equation 1) <cm3> Rhole <cm> (½ diameter) Vhole (equation 2) <cm3> Vb - h (equation 3) <cm3> ρwood (equation 4) <g/cm3> MS 20 Laboratory Revised on 6/17/2017 Density, Specific Gravity, Archimedes and Isostasy Page 1 of 7 Archimedes' Principle states that a floating body will displace its own weight of fluid. Are the masses of the blocks the same as the masses of water each displaces? If there is a difference, what are the likely sources of error? B. Modeling the Continental and Oceanic Lithosphere Pine Block Oak Block Depth of water <cm> Volume of water <cm3 or mL> Mass of water <g> Mass of block <g> Combined masses <g> (water column + wood block) Depth of water / no. blocks <g> Mass of water / no. blocks <g> Again, according to Archimedes' Principle the pressure (or the total weight) acting on the bottom of the tank (or at some depth in the asthenosphere) should not change as more floating masses are added; i.e., the combined masses of each of the wood blocks and the water columns beneath them should be the same as the total mass of the open water. Is this true here? Again, try to account for likely sources of error. MS 20 Laboratory Revised on 6/17/2017 Density, Specific Gravity, Archimedes and Isostasy Page 2 of 7 Figure 6 shows our model of the earth's crust using two different types of wood of to represent the two different types of crust. Assume you shaved some wood off the top of the pine block (representing continental erosion). What would happen to the pine block? Explain. Depth of water under two pine blocks <cm> Volume of water column <cm3 or mL> Mass of water column <g> Total mass of two pine blocks <g> Combined masses of blocks and water column <g> MS 20 Laboratory Revised on 6/17/2017 Density, Specific Gravity, Archimedes and Isostasy Page 3 of 7 Is the total mass acting on the bottom of the aquarium approximately the same as in the previous calculations? Again, try to account for likely sources of error? MS 20 Laboratory Revised on 6/17/2017 Density, Specific Gravity, Archimedes and Isostasy Page 4 of 7 Gravity and time, aided by various processes of physical and chemical weathering, removes rock from higher continental elevations and transports it to lower elevations, ultimately to the ocean floor. For every meter of rock removed from a mountain range, would you expect the elevation to decrease by one meter? Explain. What happens to the oceanic crust as water, ice and wind continuously deliver and deposit continental sediments? Explain. C. Density and Specific Gravity of Rocks GRANITE BASALT PERIDOTITE Mass in air Mass in water Massair - Masswater Rock volume (equation 5) Rock density (equation 4) MS 20 Laboratory Revised on 6/17/2017 Density, Specific Gravity, Archimedes and Isostasy Page 5 of 7 Can you think of another way to measure the volume of the rock specimens? D. Determination of total asthenosphere weight under ocean crust 5.0 x 105 cm x A. Depth of water 10 x 105 cm exerted at a x Water density x Basalt density x 1.0 cm x Peridotite density 1.0 cm 1.0 cm = Width (W) x Length (L) x C. Depth of mantle 1.0 cm fixed depth within the Length (L) x B. Depth of ocean crust 135 x 105 cm mass 1.0 cm = Width (W) x Length (L) 1.0 cm = Width (W) Total weight under ocean (A + B + C) = weight under continental crust 30 x 105 cm x D. Depth of crust 120 x 105 cm x Granite density x Length (L) x E. Depth of mantle 1.0 cm x Peridotite density 1.0 cm 1.0 cm = Width (W) x Length (L) 1.0 cm = Width (W) Total weight under continent (D + E) = weight under mountains 55 x 105 cm x F. Depth of crust 100 x 105 cm G. Depth of mantle x Granite density x x Length (L) x Peridotite density 1.0 cm 1.0 cm Length (L) 1.0 cm Width (W) x 1.0 cm Revised on 6/17/2017 = Width (W) Total weight under continental mountains (F + G) MS 20 Laboratory = Density, Specific Gravity, Archimedes and Isostasy = Page 6 of 7 During ice ages slightly cooler temperatures at mid-to-high latitudes cause less snow to melt in spring and summer than accumulates in winter. Over many years this ice piles up to form continental glaciers that can exceed 2 kilometers in thickness. Glacial ice has a density of about 0.9 g/cm3, just below that of water, and about 1/3 that of granite. What would be the effect of a 2000 meter thick ice sheet on the continent? What would happen when the ice melted? The total weight under the continents should precisely equal the weight under the ocean basin. The calculations, although close, don't really match. What does this tell us about our simple three-rock model? Explain. The last ice age ended in northern Europe and in North America approximately 10,000 years ago, yet there is excellent evidence that the Scandinavian peninsula (which includes Norway, Sweden and Finland) is still uplifting rapidly. From this information, what can we conclude about the physical properties of the asthenosphere? MS 20 Laboratory Revised on 6/17/2017 Density, Specific Gravity, Archimedes and Isostasy Page 7 of 7