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isostacy
ch 15-19 internal processes
| Question | Answer |
|---|---|
| what is isostacy | the balance/equilibrium between adjacent blocks of lithosphere (the Earths’ crust) which float on the asthenosphere (a fluid/ plastic mantle). |
| Lithosphere less dense than asthenosphere so the crust floats on the denser mantle. | |
| Like blocks of wood floating on water, blocks of lithosphere (e.g. tall block = mountain range, or shorter block = continental lithosphere) with float on asthenosphere. Blocks will rise or sink until: | Weight of the fluid displaced by block = the total weight of the block Equilibrium or Isostatic balance |
| # Like blocks of wood floating on water, blocks of lithosphere (e.g. tall block = mountain range, or shorter block = continental lithosphere) with float on asthenosphere. Blocks will rise or sink until: | So less dense block of wood (like Earth’s crust) will not be fully submerged because the block’s total weight is the same as smaller, denser volume of fluid. |
| # Like blocks of wood floating on water, blocks of lithosphere (e.g. tall block = mountain range, or shorter block = continental lithosphere) with float on asthenosphere. Blocks will rise or sink until: | The block will float at that level ie. has undergone Isostatic adjustment = moved vertically to reach equilibrium |
| # Like blocks of wood floating on water, blocks of lithosphere (e.g. tall block = mountain range, or shorter block = continental lithosphere) with float on asthenosphere. Blocks will rise or sink until: | So: tall mountain range blocks will extend the mountain root deep into the mantle shorter continental blocks don’t extend their base (root) as far into the mantle |
| # Like blocks of wood floating on water, blocks of lithosphere (e.g. tall block = mountain range, or shorter block = continental lithosphere) with float on asthenosphere. Blocks will rise or sink until: | Lithosphere (crustal rocks (in some places overlying ocean)can be thought of as separated into vertical columns) Each vertical column has the same pressure at its base Each column will rise or sink to this depth of equal pressure regardless of depth |
| # Like blocks of wood floating on water, blocks of lithosphere (e.g. tall block = mountain range, or shorter block = continental lithosphere) with float on asthenosphere. Blocks will rise or sink until: | Unlike blocks of wood, lithosphere is not divided into separate blocks moving freely of each other Instead, lithosphere bends in broad uplifts and downwarps. |
| Isostatic adjustment (vertical change to reach equilibrium) can occur in these ways: | Erosion from mountains etc., deposits sediment on lower plains. This decreases weight of mountain section of crust causes it to rise Increase in weight of lower area covered in new sediment makes it sink. |
| Isostatic adjustment (vertical change to reach equilibrium) can occur in these ways: | Formation and melting of glaciers Weight of thick ice sheets causes lithosphere beneath them to sink After melting, the crust rises back up = crustal rebound (like lying on a sofa!) |
| Isostatic adjustment (vertical change to reach equilibrium) can occur in these ways: | To rise of sink, requires the asthenosphere to be ductile to allow movement |
| Volcanism | volcano erupts, less weight for volcano column so it will rise over time until in equilibrium/isostatic balance Lava&rock from volcano falls lower areas, adding weight so areas surrounding volcano will sink over time until in equilibrium/isostatic balanc |
| Mountain building | As mountain range pushed up, weight increases and that column of lithosphere with slowly sink until reaches isostatic balance, at same time mountain building occurring. |
| Erosion | Mountains erode, becoming smaller so mountain column will rise over time Debris from erosion settles in lower areas around mountains. Increase in weight here causes the plains to sink until reaches equilibrium/ isostatic balance |
| Glaciation | + Glacier forms adding weight to lithosphere so that part will sink over time + As glacier then melts, lithosphere will rise (crustal rebound) as less weight now |
Created by:
maximus