Mike Tuke’s

Isostasy Analogies TE How does the level of a boat in water change when people get in or out of it? How does the level of your mattress change as you get into and then out of bed. Sponge D Several different weights are placed on a large piece of very soft sponge 30cm by 30cm by 10cm. which represents the mantle. They sink to different levels just as different sizes of mountains have different depths of roots. Wood and water D A glass tank is filled with water. A wooden block is put in it and the further blocks of the same size placed on top.  The changing level of the top and bottom of the first piece of wood is noted.  The pieces of wood are then removed one by one. Isostasy E P F 40 min As above but students measure the changing levels and the thickness of the blocks of wood added. From their data they work out (or confirm) the formula that relates the changing levels of the surface to the density of the wood and water. Effects of Isostasy   A or D F 60 min This is a series of activities to show how isostatic adjustment affects the height and shape of the land and the age of the rocks at the surface. This can be run as a circus of activities for students or can be a series of demonstrations.  In all activities the crust is represented by blocks of wood and the mantle by the water. The following are covered: 1  The effect of thickness and of density of the crust on the height of the earth’s surface. 2  Explaining why the top of the oceanic crust is lower than the top of the continental crust 3   Explaining the shape of rift valleys 4  The effects of erosion and deposition 5 The effects of ice sheets, volcanoes, and mountain building 6  How isostasy and erosion level explain the age of the rocks at the surface 7  The formation of atolls and guyots      Isostasy and gravity on a volcanic island P 10 min F Students place a triangle of wood representing a volcano onto a sheet of foam which is floating on water.   They work out how the pull of gravity varies over the volcano and surrounding trough.  In a second activity they work out how the pull of gravity varies as the volcano sinks due to isostatic adjustment. Slow sinking D  Use this as demonstration to show that isostatic adjustment is a slow process and that there is a delay between the adding of weight to the crust and the sinking due to isostatic adjustment. A glass sided box 40cm by 10cm by 10cm filled with “memory foam”.  A heavy weight is placed on top of the foam and it takes 20 min or so to sink.  The weight that I use is a triangular shaped piece of lead 9.5cm wide by 9.5cm long by 5cm high made by pouring molten lead into the corner of a wooden box. The formation of atolls, magnetic model D F This is a magnetic model. The background is a section showing the air, sea and oceanic crust.  A volcano is moved slowly downward as it sinks by isostatic adjustment into the crust and the coral reef is seen to grow upward. Eventually the volcano sinks below sea level and an atoll is formed. i  

Earth Science Activities and Demonstrations