  The southern hemisphere of comet 67P/Churyumov-Gerasimenko (67P) became
observable by the Rosetta mission in March 2015, a few months before cometary
southern vernal equinox. The Anhur region in the southern part of the comet's
larger lobe was found to be highly eroded, enriched in volatiles, and highly
active. We analyze high-resolution images of the Anhur region pre- and
post-perihelion acquired by the OSIRIS imaging system on board the Rosetta
mission. The Narrow Angle Camera is particularly useful for studying the
evolution in Anhur in terms of morphological changes and color
variations.}{Radiance factor images processed by the OSIRIS pipeline were
coregistered, reprojected onto the 3D shape model of the comet, and corrected
for the illumination conditions. We find a number of morphological changes in
the Anhur region that are related to formation of new scarps; removal of dust
coatings; localized resurfacing in some areas, including boulders
displacements; and vanishing structures, which implies localized mass loss that
we estimate to be higher than 50 million kg. The strongest changes took place
in and nearby the Anhur canyon-like structure, where significant dust cover was
removed, an entire structure vanished, and many boulders were rearranged. All
such changes are potentially associated with one of the most intense outbursts
registered by Rosetta during its observations, which occurred one day before
perihelion passage. Moreover, in the niche at the foot of a new observed scarp,
we also see evidence of water ice exposure that persisted for at least six
months. The abundance of water ice, evaluated from a linear mixing model, is
relatively high (> 20%). Our results confirm that the Anhur region is
volatile-rich and probably is the area on 67P with the most pristine exposures
near perihelion.
