Fire and alluvial chronology in Yellowstone National Park: Climatic and intrinsic controls on Holocene geomorphic processes

Abstract

We employed a systemwide approach, a large and robust set of radiocarbon ages, and modern process analogs to interpret the Holocene history of forest fire-related sedimentation and overall alluvial activity in northeastern Yellowstone National Park. Debris-flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire-related sedimentation within valley-side alluvial fans of Soda Butte Creek. Fire-related deposits make up approximately 30% of the late Holocene fan alluvium. Fifty 14 C ages on fire-related events cluster within the intervals of 3300 -2900, 2600 -2400, 2200 -1800, and 1400 -800 yr B.P. and suggest earlier episodes of large fires and fan aggradation around 7500, 5500, and 4600 -4000 yr B.P. A major pulse of fire-related debris-flow activity between 950 and 800 yr B.P. coincided with the height of the widely recognized Medieval Warm Period (ca. A.D. 1050 -1200). Instrumental climate records over the last ϳ100 yr in Yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods, enhancing the potential for severe short-term drought, major forest fires, and storm-generated fan deposition. Along lower Soda Butte Creek, fill-cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca. 8000 yr B.P. (terrace level T1a), 7000 -5600 (T1b), 3100 -2600 (T2), 2000 -1300 (T3), and post-800 yr B.P. (T4). These periods coincide with overbank sedimentation on Slough Creek and the Lamar River but alternate with intervals of fire-related fan deposition, implying a strong climatic control. Local paleoclimatic data suggest cooler, effectively wetter conditions during terrace tread formation. In warmer, drier intervals, reduced average runoff in axial streams results in meander-belt narrowing; concurrent channel incision may be caused by infrequent large floods. Greater resistance to downcutting, however, allowed fewer terraces to be formed along Slough Creek and the Lamar River. Alluvial systems in northeastern Yellowstone show a clear response to millennial-scale climatic cycles, wherein alluvial fans aggrade and prograde over flood plains in drier periods. Axial streams widen their flood plains and trim back the fans during wetter periods. ''Smallscale'' climatic fluctuations of the Holocene thus had substantial impact on postglacial landscapes in northeastern Yellowstone.

Over 16,000 Years of Fire Frequency Determined from AMS Radiocarbon Dating of Soil Charcoal in an Alluvial Fan at Bear Flat, Northeastern British Columbia

“…Millspaugh et al (1998) suggested a trend related primarily to solar insolation, though more detailed dating suggests a link to millennial-scale phenomena (see also Meyer et al 1995). The results of Meyer et al (1995), discussed by Meyer and Pierce (2003), suggest an anti-correlation with Bond cycles and also a response to century-scale events such as the MWP and the Little Ice Age.…”

“…in Yellowstone (Meyer et al 1995;Millspaugh et al 2000), Idaho (Meyer et al 2001), Oregon (Long et al 1998), southwestern BC (Gavin et al 2003b;Hallett et al 2003a;Lertzman et al 2002), and southeastern BC (Hallett and Walker 2000;Hallett et al 2003b). This signal appears less marked in the tropics (Horn and Sanford 1992;Turcq et al 1998) and in other mid-latitude regimes, such as in eastern Canada (Carcaillet et al 2001) and New Zealand (Molloy et al 1963).…”

“…This distribution was obtained by summing the probability ranges of all the calibrated 14 C ages. We summed the probability distributions derived from Calib 5.0 (Reimer et al 2004), which is the same method employed by Meyer et al (1995) and Pierce et al (2004), except they used an older version of the calibration. This plot shows striking increases in fire at several periods (e.g.…”

“…The long-term record of forest-fire history has been studied in a number of regions (Meyer et al 1995(Meyer et al , 2001Cwynar 1987;Long et al 1998;Hallett et al 2003a,b;Millspaugh et al 2000;Horn and Sanford 1992;Turcq et al 1998;Lertzman et al 2002;Hallett and Walker 2000;Pierce et al 2004) of the world, but there is little information on fire history in more northerly regions of Canada. There are basically 2 kinds of studies: 1) direct measurement of charcoal found in alluvial and colluvial deposits (e.g.…”

“…There are basically 2 kinds of studies: 1) direct measurement of charcoal found in alluvial and colluvial deposits (e.g. Meyer et al 1995Meyer et al , 2001Lertzman et al 2002;Pierce et al 2004); and 2) studies of the charcoal record found in lake sediments (e.g. Long et al 1998;Millspaugh et al 2000).…”