D. Mccarroll et al., SPATIAL AND TEMPORAL PATTERNS OF LATE HOLOCENE ROCKFALL ACTIVITY ON ANORWEGIAN TALUS SLOPE - A LICHENOMETRIC AND SIMULATION-MODELING APPROACH, Arctic and alpine research, 30(1), 1998, pp. 51-60
Largest lichens (genus Rhizocarpon) were measured on 2800 boulders sam
pled systematically at 28 sites on a thin triangular talus. Sites with
similar lichen-size frequency distributions were grouped and used to
interpret the temporal and spatial patterns of rockfall supply. Most o
f the slope yields size-distributions of largest lichens that reflect
the history of rockfall activity over at least the last 400 yr. A gene
ral increase in surface age diagonally downslope suggests boulders are
supplied by rockfall rather than avalanching, with no evidence of pos
tdepositional redistribution. At one corner of the talus foot the lich
en-size distributions have reached equilibrium, suggesting negligible
supply of boulders during the late Holocene. Sites at the apex of the
talus are dominated by small lichens. Simulation modeling is used to r
econstruct possible temporal patterns of debris supply to different pa
rts of the talus, and competing models are tested by estimating the th
ickness of talus predicted to have accumulated during the Holocene. Th
e normal rate of rockfall during the late Holocene is estimated to res
ult in burial of about 4% of the talus surface each 25 yr. Rates of ro
ckfall supply during the 18th century, the coldest phase of the Little
Ice Age, are estimated to have been almost five times the normal late
Holocene rate. Results are consistent with talus formation under peri
glacial conditions during the Holocene; a paraglacial origin is unnece
ssary.