Grant Meyer

We employed 14C dating of alluvial-fan deposits in ponderosa pine and mixed-conifer forests of the Sacramento Mountains, New Mexico to document Holocene fires and related geomorphic impacts. Rapid aggradation by charcoal-rich debris flows occurred in the middle Holocene (5800—4200 cal. yr BP), indicating episodic sedimentation following severe fires. Fire-related deposition virtually ceased ~4200 cal. yr BP, with most fan deposits indicating slower aggradation with cumulic soil development until 1800 cal. yr BP. From 1800 to 500 cal. yr BP, fire-related sedimentation increased again, although not to middle Holocene levels. A peak in fire-related sedimentation c . 650 cal. yr BP corresponds to widespread severe drought in the southwestern USA. Limited fire-related sedimentation is evident from 500 to 100 cal. yr BP, consistent with `Little Ice Age' climate and tree-ring records indicating frequent low-severity fires, although at least one severe fire burned in this interval. Increased fire-related sedimentation corresponds to generally warmer conditions. We infer that higher climate variability was also involved, including multidecadal wet periods that limited surface fires and allowed stand densities to increase, promoting severe fires in subsequent severe droughts. Fire has contributed significantly to Holocene valley aggradation. Local fan channel incision followed recent fires, but major nineteenth—twentieth century arroyo cutting appears unprecedented during the Holocene.

The morphologies of some martian gullies appear similar to terrestrial features associated with debris flow initiation, erosion, and deposition. On Earth, debris flows are often triggered by shallow subsurface throughflow of liquid water in slope-mantling colluvium. This flow causes increased levels of pore pressure and thus decreased shear strength, which can lead to slide failure of slope materials and subsequent

... Climate drivers of regionally synchronous fires in the inland Northwest (1651–1900) Emily K. Heyerdahl, Donald McKenzie, Lori D. Daniels, Amy E ... study identifies the relationships between climate vari-ability and fire occurrence and extent in the southern Cas-cades before the ...

... The Rio Gallina, which enters the Rio Chama a few kilometers above the study reach, may have contributed a significant propor-tion of this ... AD 1400-1880), Paria River Basin and southern Colorado Plateau, United States: Geological Society of America Bulletin, v. 114, p. 1550 ...

ABSTRACT Volcano-tectonic deformation has been measured within the Yellowstone caldera using precision leveling techniques. The shorelines represent originally horizontal planes, accumulated deformation of which can be observed as vertical displacement and tilt. Dating of the shorelines allows the calculation of average rates of deformation since and between episodes of shoreline formation. Shoreline elevations projected to perpendiculars to isolines on contemporary uplift correlate well for 12 km across the perpendiculars. Projections to parallels are nearly horizontal for 5 km. 1985 fieldwork will extend this line to 20 km. Both correlations imply that the pattern of contemporary uplift is an accurate model for late Holocene deformation. Maximum late Holocene rates of deformation, as determined form minimum ¹⁴C dates, are 50-75% of contemporary rates. This suggests that late Holocene deformation has 1) been episodic (50-75% of the time), 2) been oscillatory (75-90% up, 10-25% down), or 3) occurred at an increasing rate through time. Tilt and uplift rates are similar, implying little downcutting at the outlet, and rates between shorelines are similar to those since shoreline formation, implying nearly constant average rates of deformation in the past 2500 years. Local deformation has been significant throughout the late Holocene. Episodic deformation in a graben 1 km across has controlled the location of the lake outlet, thus water level. Sharp local warping has deformed some shorelines by 1 mm/yr. These faults may relate to volcanic processes or to the regional tectonic regime.

Both modern observations and Holocene fire proxy records indicate that the magnitude and timing of wildfires is significantly affected by climatic change. Continental-scale drought episodes appear to be linked strongly to temperature, so that in 2002 and other recent warm years, major fires occurred in a variety of coastal and interior forest ecosystems despite regional precipitation differences and land management effects. We examine the timing of Holocene fires in central Idaho and Yellowstone National Park through interpretation and radiocarbon-dating of burned soil surfaces and fire-related sediments preserved in small alluvial fans. A large sample of alluvial fan stratigraphic sections within each region provides an essentially continuous and high-resolution record of fire-related sedimentation, including indications of fire severity. Major fire-related sedimentation occurred in cool, high-elevation mixed-conifer forests of Yellowstone between 1250 and 730 cal yr BP. In lower and warmer ponderosa forests in Idaho, at least 4 sites experienced fire-induced debris flows between ~950 and 730 cal yr BP. Dates from these fire-related sedimentation events correspond to the Medieval period, as does evidence of synchronous fires in diverse climatic zones and ecosystems from other studies in the western U.S. Throughout the Holocene, minima in fire-related sedimentation in Yellowstone correspond with maxima of ice-rafted debris and cool episodes on ~1500 year cycles in the North Atlantic (Bond et al., 1997). At these times, floodplain widening along streams in Yellowstone and low-severity fires in Idaho are consistent with higher effective moisture and cooler conditions. Even though these studies cannot reconstruct absolute variations in temperature and precipitation, they reflect millennial-scale temperature variations in the western U.S. that are clearly consistent with the North Atlantic cycles. Other paleoclimate proxies from the western U.S. including lake-level fluctuations, paleovegetation records, and glacial advances also provide evidence of notable warm and dry episodes in the Medieval period as well as Little Ice Age cooling. Nonetheless, late 20th-century warming and fires may exceed previous episodes in extent and severity.

Quaternary geology and ecology of the greater Yellowstone area Authors and Leaders: Kenneth L. Pierce, US Geological Survey, Bozeman, MT 5971 Don G. Despain, US Geological Survey, Bozeman, MT 5971 Cathy Whitlock, Univ. of Oregon, Con'allis, OR, 97403-1251 ...

WATT, Paula M. 1, MEYER, Grant A. 2, JAMES, Stacey 1, JOE, Louis 1, PABLO, Daniel 1, TOM, Leonard 1, TSETHLIKAI, Charlotte 1, and TULLEY, Crystal 1,(1) Math and Science, Univ of New Mexico-Gallup, 200 College Road, Gallup, NM 87301, pwatt@ gallup. unm. ...

Climate is commonly assumed to be an important factor influencing weathering, erosion and landscape evolution, but few studies have quantitatively assessed differences in geomorphology associated with minor but persistently different moisture and temperature conditions. In northeastern Arizona, we have studied several small ( ˜0.5 km2), semi-arid eastward-draining basins where topography has induced different microclimates on north- and south-facing canyon slopes.

ABSTRACT It has been asserted that beaver ( Castor canadensis) damming has sustained long-term aggradation and exerted a dominant control on the morphology of small streams over much of North America. However, data on the temporal and spatial dimensions of beaver influence are extremely limited. Using beaver pond deposits and berms (abandoned dams), we document geomorphic effects of beavers on first- to fourth-order streams in semiarid-subhumid northern Yellowstone National Park, USA. Beavers were ubiquitous in the early 20th century, but are currently rare. Some formerly dammed streams have become ephemeral in recent droughts, suggesting that climate may be a significant factor controlling beaver occupation. Radiocarbon dating of wood preserved in pond deposits and berms shows notable periods of beaver activity 3655-3855, 1555-955, and 455-150 cal yr BP, but a distinct lack of activity 950-700 cal yr BP during the Medieval Climatic Anomaly, a time of severe multidecadal droughts in Yellowstone and the western USA. The spatial scale over which beavers incurred significant aggradation is controlled largely by geomorphic settings conducive to damming. Low-gradient (0.07 to 0.001) reaches with contributing areas of 4 to 70 km2 are typical for dam sites. Reaches with downstream valley constrictions are most susceptible to aggradation. Only a small fraction of the total stream length in the study area has experienced significant aggradation attributable to beaver damming, as shown by accumulations of sand and finer sediment of up to 3 m, thicker than typical overbank sediments. These sediments locally contain evidence of ponding in laminations, gleying, and high organic content. Many reaches show no evidence of any net aggradation since deglaciation. Many beaver-aggraded reaches are now incised, typically 1.5-2 m and up to 3 m. Some reaches have early Holocene (ca. 10150-8000 cal yr BP) terraces with treads ~2 m above current bankfull level, underlain by both gravelly and fine-grained fill deposits showing little evidence of ponding. Overall, these observations suggest that very high beaver populations of the early 20th century were an anomaly and that their presence in the Holocene was intermittent, with only local major impact. This counters the assumption that most stream reaches in this and similar systems have been degraded largely because of beaver abandonment.

The Sacramento Mountains contain numerous small alluvial fans produced by low-order tributaries in ponderosa pine dominated mixed-conifer forests. Arroyos up to 12 m deep in the main valleys expose a 9000 year record of geomorphic change within these fans. Identification and dating of fire-related fan deposits allows us to examine the changing importance of fire-related geomorphic processes through time, and

Increased wildfire activity has accompanied late 20th-century to present warming across the diverse conifer forests of western North America. In ponderosa pine forests in particular, large, severe wildfires and ensuing erosion and debris flows appear unprecedented in light of tree-ring fire-scar records, and are often attributed to increased stand density following Euro-American settlement and fire suppression starting in the late