*DYNAMICS OF DEBRIS FLOWS AND ROCK
AVALANCHES*

**Abstract:** DYNAMICS OF DEBRIS FLOWS AND ROCK
AVALANCHES Diverse geophysical mass flows involve
rapid, gravity-driven motion of grain-fluid mixtures across
three-dimensional terrain. Dense geophysical mass flows (with
grain volume fractions larger than about 0.4) dissipate energy primarily
through direct grain-to-grain contacts mediated by intergranular fluid
pressure. Such flows include water-saturated debris flows and
rock avalanches in which the interagranular fluid consists largely of
air. This specturm of flows can be modeled using a
theoretical framework that is essentially a revision and generalization
of the well-known Savage-Hutter model of granular avalanche motion
resisted by Coulomb friction. The model revisions described
in this lecture include (1) use of rectangular Cartesian coordinate
system rather than a fitted curvilinear coordinate system, (2) explicit
estimation of vertical accelerations that modify the effect of gravity
on internal stresses and basal tractions, (3) evaluation of Coulomb
stresses using a finite-element calculation that enables stress
components to be resolved into any coordinate system, including a
rectangular Cartesian system. Effects of pore-fluid pressure and
physical experiments that motivate model formulation and test model
predictions are also
discussed.&