Controls on the rates and products of particle attrition by bed-load collisions

Abstract

Abstract. River rocks round through the process of impact attrition, whereby energetic collisions during bed-load transport induce chipping of the grain surface. This process is also important for bedrock erosion. Although previous work has shown that impact energy, lithology, and shape are controlling factors for attrition rates, the functional dependence among these quantities is not settled. Here we examine these factors using a double-pendulum apparatus that generates controlled collisions between two grains under conditions relevant for bed-load transport. We also determine the grain size distributions (GSDs) of the attrition products. Two experimental results appear to support previous treatments of impact erosion as brittle fracture: (i) mass loss is proportional to kinetic energy, and this proportionality is a function of previously identified material properties; and (ii) attrition-product GSDs are well described by a Weibull distribution. Chipping results from the development of shallow and surface-parallel cracks, a process that is distinct from bulk fragmentation that occurs at higher energies. We suggest that Hertzian fracture is the dominant mechanism of impact attrition for bed-load transport. We also identify an initial phase of rapid mass loss in which attrition is independent of energy and material properties; this is a shape effect associated with removal of very sharp corners. The apparent universality of both mass loss curves and attrition-product GSDs requires further investigation. Nonetheless, these findings are useful for interpreting the contribution of in-stream attrition to downstream fining and the production of sand resulting from bed-load transport of river pebbles.

Sand, Gravel, Cobbles, and Boulders: Detrital Thermochronology Shows that One Size Does Not Tell All

“…The breakdown of sediment after it is produced on slopes adds a complication to interpreting initial sediment size distributions from the thermochronological portrait of sediment presented here. However, abrasion and fracturing, the two main modes of sediment breakdown in streams, can be modeled mechanistically using theory and data from experiments and field observations (e.g., Attal & Lavé, 2009; Le Bouteiller et al., 2011; Litwin Miller & Jerolmack, 2021; Szabó et al., 2015). It should be possible to combine these models with (U‐Th)/He ages in stream sediment to better resolve and explain the spatial variation in size distributions of sediment produced on slopes.…”

“…In mountain landscapes, where many of these factors often vary across individual catchments, different sediment sizes at the outlet may reflect sediment production from different parts of the catchment, where lithologic, climatic, and topographic conditions favor different sizes. Sediment sizes at the outlet are also likely influenced by the breakdown of coarser particles during transport by abrasion, chipping, and fracturing (Attal & Lavé, 2009; Lavarini et al., 2018; Litwin Miller & Jerolmack, 2021). Breakdown rates and the size distributions of breakdown products have been shown to depend on lithology (Kodama, 1994b), degree of chemical weathering (Goodfellow et al., 2016; Heller et al., 2001), and energy of transport (Arabnia & Sklar, 2016; Attal & Lavé, 2009), and can affect grain size distributions even in durable lithologies and over short distances (Dingle et al., 2017; Kodama, 1994a).…”

Downstream rounding rate of pebbles in the Himalaya

“…We use the term "fragmentation" to exclusively describe significant breakdown of a grain into large pieces (e.g. Miller and Jerolmack, 2021). All of these processes act on sediment particles while they are being carried by water current in rivers, leading to a reduction in their size and alteration of their shape.…”

Investigating effects of initial grain size distribution on rock wear rate and shape change due to abrasion

“…These collisions result in fragmentation from impact with the bed floor and other rock grains. As a consequence of collisions, rocks begin to lose their protruding areas, mass, and overall angularity as defined elsewhere in the literature (Litwin Miller & Jerolmack, 2021).…”

“…The term abrasion describes the process of rock being eroded away due to fiction, whereas the term attrition refers to energetic collisions due from sediment transport during river transport (Litwin Miller & Jerolmack, 2021). As rock particles are subjected to abrasion they slowly start to change shape as their protruding areas are worn away (Domokos et al, 2014).…”