The Himalaya is the most impressive example on earth of an active
collisional orogen. It combines rapid crustal shortening and thickening,
intense denudation driven by the monsoon climate, and frequent very large
earthquakes along an incomparably long and high mountain arc. It has
therefore been the focus of a variety of investigations that have addressed
various aspects of mountain building on various timescales. Geological and
geophysical studies give some idea of the structure of the range and physical
properties at depth. The long-term geological history of the range, over say
several millions to a few tens of millions of years, has been documented by
structural, thermobarometric, and thermochronological studies. Morphotectonic
investigations have revealed its evolution over several thousands or
tens of thousands of years; and geodetic measurements and seismological
monitoring have revealed the pattern of strain and stress built-up over
several years. This chapter is an attempt to show that the results of these
investigations can be assembled into a simple and coherent picture of the
structure and evolution of the range. The author also intends to illustrate
the interplay between these various processes operating at different timescales.
One important example of processes that interact via feedback
mechanisms is particularly clear in the Himalaya: the thermal structure of
the range, which is a result of the long-term crustal deformation and pattern
of exhumation, governs, through its influence on rheology, the pattern of
deformation as well as the seismic behavior of the range-bounding thrust
fault.