In February 2010, 19 fatalities and economic damage
were caused by a regional landslide episode in the state of
Michoacán, México. The municipalities of Angangueo, Ocampo,
Tiquicheo de Nicolás Romero, Tuxpan, and Tuzantla were
severely damaged, with Angangueo being the most affected. The
event involved a series of debris flows, of which four were the
most significant; these four caused 16 deaths in addition to
considerable damage to roads, electricity, and the water supply
system, with indirect consequences in crop production, cattle
farming, and tourism. The area affected by these four flows was
calculated as 282km2
, with an estimated 697,346m3 of mobilized
material. General observations indicated that the initiation
sources of the debris flows were on deforested zones. The present
research is concentrated on the Angangueo basin, an area situated
within the Monarch Butterfly Biosphere Reserve. Given the lack of
rain gauges in the area of interest, records from neighboring
points were used to build a comprehensive overview of the
extreme precipitation event that triggered the devastating debris
flows. The nearest rain gauge, Laguna del Fresno, situated 21km to
the south, recorded 204mm of rainfall from 1 to 5 February,
equivalent to 30% of the mean annual rainfall. Moreover, during a
24-h period the El Bosque rain gauge recorded 144.5mm of
precipitation, the equivalent of 2,270% of the mean rainfall for the
same month (6.36mm). The occurrence of a hailstorm preceding
the rainfall event is notable; conditions in the superficial soil layer
would have included an increased pore water pressure. Presumably,
before the 2,000-year return period extreme rainfall event,
thawing of hail and consequent moisture and/or pore-pressure
increase result in decreased frictional strength. This paper
presents a spatial analysis of the distribution of these landslides,
mainly debris flows, as well as general observations on the
triggering mechanism, the strength properties of the materials
involved, and the societal impact.