Figure 5 - uploaded by Christian González
Content may be subject to copyright.
Historic position of the Salt, Verde and Gila Rivers portrayed on a public domain map produced by the Salt River Project in the 1930s. Locations 1a-1d identify the piedmonts shown in Figures 1a-1d. Note that Sierra Estrella drainages have the Gila River as their modern base level, but drainages on the west side of the range have a much further distance to travel to the Gila River than those on the north or east sides.
Source publication
Ephemeral channels incise into the piedmonts (both alluvial fans and pediments) of the northeastern Sonoran Desert, USA. Located around metropolitan Phoenix, this tectonically quiescent region experienced only aggradation in endorheic structural basins throughout the Pliocene. A wave of aggradation then followed Salt and Gila river integration at t...
Contexts in source publication
Context 1
... pediments (a and c) and desert alluvial fans (b and d) experience incision in the tectonically quiescent northeastern Arizona BRP. The location of these piedmonts are indicated in Figure 5. Scale information on the length of each piedmont is provided below. ...
Context 2
... ongoing Pliocene aggradation Skotnicki et al., 2020b) in the Luke and Higley basins (Figure 3), the normal expectation would be to see channel infilling on pediments and alluvial fans entering these basins. However, the exact opposite condition exists for piedmonts fronted by the Salt and Gila rivers (Figures 4-5), including the Papago Buttes, Phoenix Mountains, San Tan Mountains, South Mountains, and Sierra Estrella range (Figure 1(a,b); Figure 6). ...
Context 3
... the spatial scale of a shifting river channel has never been explored at the ca. 6000 km 2 scale within the northeastern Sonoran Desert region of Arizona (Figures 3-5). ...
Context 4
... et al. (2014Larson et al. ( , 2016Larson et al. ( , 2020) studied the response of pediments to drainage integration processes just to the north and east of our study area. From the perspective of Figure 5, Larson et al. (2014Larson et al. ( , 2016Larson et al. ( , 2020) studied pediments upstream of Granite Reef Dam, or upstream of the point at which the ancestral Salt River deposits (ASRD) aggraded a mega-fan floodplain and where the Salt and Gila rivers integrated (Figure 4). Upstream of Granite Reef Dam (Figure 5), the Salt and Verde rivers experienced a complex history of base-level rise and then fall ( Larson et al., 2020) leading to pediment incision ( Larson et al., 2014Larson et al., , 2016. ...
Context 5
... the perspective of Figure 5, Larson et al. (2014Larson et al. ( , 2016Larson et al. ( , 2020) studied pediments upstream of Granite Reef Dam, or upstream of the point at which the ancestral Salt River deposits (ASRD) aggraded a mega-fan floodplain and where the Salt and Gila rivers integrated (Figure 4). Upstream of Granite Reef Dam (Figure 5), the Salt and Verde rivers experienced a complex history of base-level rise and then fall ( Larson et al., 2020) leading to pediment incision ( Larson et al., 2014Larson et al., , 2016. Downstream of Granite Reef Dam, however, range piedmonts have experienced only continuous aggradation. ...
Context 6
... base-level history of the transition from purely endorheic drainage to throughflowing rivers is portrayed in Figures 3-5. Prior to river integration, drainages in the region flowed towards playas or depocenters in the Luke and Higley basins (Figure 3). ...
Context 7
... of the ASRD led to a stream piracy event ( Larson et al., 2020;) just east of "-35 m" in Figure 4. This avulsion site is also identified as Tempe Butte-Papago Park in Figure 5 -a low spot in a bedrock ridge where the river spilled over on a ramp built of its own sediment. ...
Context 8
... Salt River's avulsion shifted the location of the Salt River's channel to the north side of South Mountains ( Figure 5) ca. 460 ka ( Skotnicki et al., 2020b) and led to the abandonment of the ASRD. ...
Context 9
... throughout the late Miocene and Pliocene as endorheic basins infilled ( Figure 3); (ii) when the Salt, Verde and Gila rivers integrated and started filling in their new river channels from 2.8 Ma to 0.5 Ma ( Figure 4); and (iii) when the Salt River experienced an avulsion to its present position north of South Mountains about 460 ka ( Figure 5). ...
Context 10
... second key summary point is that the location of local base level shifted laterally from low spots (playas or depocenters) of the Luke and Higley Basins (Figure 3) to positions right up against several of the mountains (Figures 4 and 5). For the northern and eastern sides of the Sierra Estrella range, this lateral shift brought local base level ~7 km closer to north-end pediments (Figure 1(a)) and ~20 km closer to east-side alluvial fans ( Figure 1(b)). ...
Context 11
... 1(a,b) show incision into a granitic pediment and alluvial fan, respectively, of the Sierra Estrella where the Gila River relocated base level to their toes. The piedmonts of the Phoenix Mountains and the alluvial fans of South Mountains are also incised where they face the Salt and Gila Rivers (see Figure 5 for locations). Thus, the northeastern BRP of Arizona offers an abundance of potential sites to study the effects of both base-level rise and a lateral shift in base-level position. ...
Context 12
... we could analyze incision into the same "M1" mapping unit of Demsey (1989), judged to be early to middle Pleistocene in age of deposition. In this way, we could compare incision into the same fan unit on the east and west sides, and (iv) prior research on long-term tectonic history of extensional basins in central Arizona (Spencer, 2011) and well-log research ( Reynolds and Bartlett, 2002;) provided three time "stamps" to document the history of only base-level rise of Sierra Estrella drainages: the late Miocene-Pliocene period of basin infilling ( Figure 3); the early Quaternary arrival of the Salt River and then the Gila River ( Figure 4); and the late Pleistocene avulsion of the Salt River ( Figure 5). ...
Context 13
... a classification is beyond the scope of this work. Nevertheless, we estimate a representative value for the Toothaker pediment, at the northern Sierra Estrella (Figure 1(a); Figure 5), to offer an order of magnitude of κ. This area has a granitic lithology with desert vegetation, similar to that observed, for example, in some places of northern Chile. ...
Context 14
... to the integration of the Salt River after 2.8 Ma, piedmont base levels were found over 100 m below modern elevations at the depocenters (playas) of the Luke and Higley basins (Figure 3). After arrival of the Salt and Gila rivers, base levels both rose and moved much closer to toes of Phoenix-region piedmonts (Figures 4 and 5). Thus, we hypothesize that a massive lateral shift in base level to the toes desert piedmonts could be a potential explanation for the channel incision. ...
Citations
... Prior to river integration, closed-basin piedmonts consisted of a mixture of pediments and alluvial fans (Figure 2b & 2c). The geomorphology of these desert piedmonts responded in complex ways to river integration, but the net result produced incision of both pediments and alluvial fans throughout the study area (González et al., 2022). ...
Langbein and Schumm (1958) connected precipitation to erosion in a right-skewed curve used in earth science textbooks for over six decades, where denudation increases with precipitation on the arid/semiarid limb and decreases in humid regions. Development of the catchment-averaged 10Be denudation method a quarter-century ago led geomorphologists to evaluate this hypothesis using data not influenced by the Anthropocene, with mixed findings. The Sonoran Desert in Arizona, USA, is optimal for investigating the longstanding hypothesis of increased erosion from arid to semiarid climates due to: (i) the modern orographic effect aligning elevated precipitation with altitude, mirroring Neotoma packrat midden paleoecology research for the Holocene and late Pleistocene; (ii) the region has been tectonically quiet for the residence times of analyzed 10Be ranging from ca. 8,000-110,000 years. Our significant finding echoes Langbein and Schumm's work, revealing heightened erosion along an elevation-precipitation gradient from arid to semiarid conditions. Notably, the significance of precipitation-elevation contrasts with the absence of significant correlation between 10Be denudation and attributes like slope, drainage area, relief, or landform type (e.g., alluvial fan, pediment, mountain watershed). Modern faunalturbation, increasing along this gradient, exposes more ground to rainsplash and overland flow at higher elevations, adding complexity to these results. Further insights unveil that (i) catchments in areas with substantial Quaternary base level reduction imitate tectonic effects, tripling 10Be denudation rates; (ii) basaltic boulders and cobbles yield an armoring influence; (iii) historical erosion acceleration due to urbanization and wildfires insignificantly affects 10Be denudation rates in the Sonoran Desert; and (iv) minute desert catchments yield anomalous erosion rates.
... For example, Larson et al. (2020) point to classic landforms like pediment systems (Larson et al., 2014;Larson et al., 2016) and alluvial fans in these basins that record post-integration basin-scale adjustment and are indicative of longterm basin-response to top-down integration processes. González et al. (2021) provide further evidence of the importance of drainage integration on pediment evolution in this region. Larson et al. (2020) emphasize the importance of understanding basin-wide response to integration in order to better understand piedmont/mountain front adjustment and stream terraces (Larson et al., 2010;Larson et al., 2014;Larson et al., 2016), tributary response (Gootee et al., 2016;Jungers and Heimsath, 2019), basin evolution (Roberts et al., 1994), basin sedimentation (Richard et al., 2007), carbon dioxide sequestration (Gootee, 2013), groundwater resource management (Laney and Hahn, 1986;Reynolds and Bartlett, 2002;Skotnicki and DePonty, 2020), and natural hazard mitigation (Douglass et al., 2005;Jeong et al., 2018). ...
The development of geomorphic theory regarding fluvial-system reorganization and drainage basin evolution, resulting from drainage integration, has been slow to progress since the abandonment of Davisian geomorphology in the mid-twentieth century. Central to the development of this theory is an understanding of the processes that allow rivers to cut across topographic and/or structural barriers that separate neighboring drainage basins. Barrier-crossing rivers are termed transverse drainages. Development of this geomorphic theory also includes an understanding of the basin-wide geomorphic and sedimentologic response to the establishment of a transverse drainage. Since at least the eighteenth century, geomorphic scholars such as J. Hutton, J. Playfair, J.W. Powell, G.K. Gilbert, C.E. Dutton, W.M. Davis, E. Blackwelder, C.B Hunt, and T.M. Oberlander described transverse drainages using a variety of terms like: water gaps, transverse valleys, transverse gorges, transverse river gorges, drainage anomalies, transverse trunk valleys and boxes. A resurgence of drainage-integration research in the past few decades produced a consensus that four generalized processes, and variations therein, result in drainage integration and transverse drainage establishment: Antecedence; Superimposition; Piracy/Capture; and Overflow/Spillover. Antecedence occurs when a river maintains its position through sufficient erosive power during tectonic uplift. This results in a river that has cut through the uplifted terrain. Superimposition occurs when a river incises through erodible materials, or a cover mass, and becomes locked in place across an exhumed bedrock high. Both Antecedence and Superimposition require a river that is older than the most recent exposure of the topographic and/or structural feature it now cuts through. Piracy, or Capture, occurs when a river shifts to a new and steeper gradient path, resulting from the capture and rerouting of the original drainage. Overflow, or Spillover, takes place when a basin fills up with sediment and water sufficiently to breach the lowest point in the basin divide and subsequently spills out into a neighboring drainage basin or outlet. Both Piracy and Overflow require the river to be younger than the topographic and/or structural feature the river transverses. The timing of this special issue’s publication aligns with a resurgence in interest and awareness of the importance of transverse drainages in economics, cultural history, establishment of surface and groundwater resources, distribution of aquatic and riparian biology and ecosystems, and even in understanding the history of Martian landscapes and climate. Therefore, we put forth this special issue to elucidate on our current understanding of drainage integration and the establishment of transverse drainages along with new insights into basin to basin and basin-wide response to transverse-drainage development. This special issue includes comprehensive literature reviews and original research in tectonic settings of regional extension where through-flowing transverse drainages exist, but also suggests that similar integration processes occur in a variety of settings globally.
Debris flows typically originate in mountainous watersheds. At the base of these watersheds and where not truncated by a higher order stream or discharging into a body of still water, repeated debris-flow deposition often forms semi-conical debris-flow fans. To mitigate debris-flow hazards, it is important to identify debris flow-prone watersheds and to understand their dynamics. This chapter reviews the morphology, sedimentology and dynamics of debris-flow watersheds and associated fans. Debris flow-generating watersheds are generally smaller and steeper than those dominated by floods and debris floods, and host less well-developed drainage networks. They can be roughly categorized into transport-limited systems (in which each hydroclimatic event producing high discharge triggers debris flows due to an abundance of sediment and high recharge rates) or supply-limited systems (in which debris-flow activity is limited by sediment availability and corresponding slow recharge rates). Debris-flow fans have typical lengths of 0.5–10 km and slopes of 5–15° and develop through spatio-temporal shifts of the locus of deposition through avulsion. Their surface topography and stratigraphy consist of stacked and amalgamated lobe, levee, and channel deposits, with sediment of mud to boulder grade. They provide archives of past flow processes and sediment supply indicative of past climate and environmental change. However, our ability to interpret debris-flow successions is still limited by relatively poor knowledge of how catchment geology and flow properties and composition affect resulting depositional features, from bed scale to fan scale. Recent field-based, experimental, and numerical advances on these topics are starting to fill this knowledge gap.
