Recurrent voluminous sector collapses at Volcán Barú, Panama
Julie Herrick
Abstract:
Two volcanic debris avalanches, both attributed to sector collapse at Volcán Barú, Panama, have been
identified after an investigation of deposits that covered thousands of square kilometers. A two-year
field campaign provided lithologic data and radiocarbon dates to assess the hazard implications of this
high-impact, low probability event. Remote sensing and geospatial analysis constrain the magnitude of
these events. Comparisons with examples from around the world provide context for this study and
contribute to the overall understanding of sector collapse and the resulting products.
The younger Barriles Deposit yielded two radiocarbon ages: 8590 ±50 ybp and 8000 ±30 ybp. Based on
radiocarbon lab studies of two samples, the older Caisán Deposit is at or beyond the radiocarbon range
(>43,500 ybp). From satellite imagery and field observations of debris hummocks, the total runout
length of the Caisán deposit was ~50 km covering 1190 km^2. The Barriles Deposit extended to about
45 km and covered an area of 982 km^2. Both of the debris avalanches are blanketed by pyroclastic
deposits and contain a predominance of andesitic material that apparently represents volcanic dome
rock which accumulated above the active vent at Barú. Despite heavy vegetation of the field area, 576
km^2 were analyzed and over 4000 individual hummocks were digitized from aerial photography.
Statistical analysis of hummock locations and geometries depict flow patterns over the entire debris fan
reflecting the effects of underlying topography and also help to define the limit of the Barriles deposit’s
shorter runout. The Barriles avalanche deposit has an estimated volume of 28 km^3 to 39 km^3 while
the Caisán Deposit is larger: 43 km^3 to 63 km^3.
The debris avalanches of Volcán Barú are examples of unconfined, subaerial volcanic deposits that rank
among the world’s most voluminous such as ancestral Mount Shasta, USA; Socompa, Chile/Argentina;
and Shiveluch, Russia. During emplacement, they travel at speeds ranging from 20-150 m/s (45 – 335
mph) (Morelli et al., 2010; Siebert, 2002; Voight et al., 1983) and these deposits have the capability to fill
in valleys, overtop ridges, smother lakes, and blanket tens of square kilometers. The age ranges
estimated for Baru’s sector collapses suggest that tens of thousands of years are necessary for
precursory conditions to develop before another collapse is eminent. This development potentially
consists of explosive volcanic activity and buildup of a large volume andesitic volcanic dome complex.
Currently, the modern edifice is 200-400m lower than the Barriles and Caisán summits and only 16-25%
of the edifice has been replaced since the last failure. Examples worldwide suggest that sector collapse
events are triggered by specific weakening and destabilization processes (Vallance et al., 1995). With
sufficient monitoring, steps to mitigate this extreme hazard can be successful.