Places along a river at which this quantity changes suddenly are called knickpoints. For 10 points each:
[10m] Name this quantity whose maximum stable value for a pile of a granular material is given by the tangent of the angle of repose. Regions that share their name with this quantity lie between continental shelves and continental rises.
ANSWER: slope [or gradient; accept continental slopes]
[10e] Knickpoints are exemplified by these features at which water flows over a vertical drop. These features are also known as cataracts or cascades.
ANSWER: waterfalls
[10h] Knickpoints form from and can contribute to river rejuvenation, in which a river erodes its riverbed in response to a lowering of this vertical datum. This datum is the lower limit of an erosion process.
ANSWER: base level
<Joseph Krol, Science - Earth> ~21141~ <Editor: David Bass>