We consider the energy-critical harmonic heat flow from
into a smooth compact
revolution surface of
.
For initial data with corotational symmetry, the evolution reduces to the semilinear
radially symmetric parabolic problem
for a suitable class of functions
.
Given an integer
,
we exhibit a set of initial data arbitrarily close to the least energy harmonic map
in the
energy-critical topology such that the corresponding solution blows up in finite time
by concentrating its energy
at a speed given by the
quantized rates
in accordance with the formal predictions of van den Berg et al. (2003). The case
corresponds
to the stable regime exhibited in our previous work (CPAM, 2013), and the data for
leave on a manifold
of codimension
in some weak sense. Our analysis is a continuation of work by Merle, Rodnianski, and
the authors (in various combinations) and it further exhibits the mechanism for the
existence of the excited slow blow-up rates and the associated instability of these
threshold dynamics.