Blocked by boulders: Examining the roles of climate, fluvial thresholds and sediment flux in slowing bedrock incision on the Hawaiian Islands 

2026-03-14

Tectonic uplift is the primary control on bedrock river incision; however, in places where uplift is absent, such as the Hawaiian Islands, other factors including climate, lithology, sediment flux, fluvial thresholds, baselevel history, and time become crucial to understanding the form and incision history of streams. Ferrier et al. (2013) argued that streams on Kauai show a linear relationship between unit stream power and incision rate with a negligible incision threshold. However, large boulders that choke Kauai’s streams suggest significant incision thresholds, and young lavas at river level suggest that incision has been negligible for ~2 Myr. We suggest that these channels are at a critical threshold set by climate, fluvial thresholds, and sediment flux that prevents them from further incising into bedrock. We present 7 new Ar-Ar ages of young lavas emplaced within Kauai’s canyons along with an extensive grain size dataset spanning 22 catchments, and 17 new catchment-averaged erosion rates (36Cl in magnetite) from catchments on Kauai and West Maui. Our results show that the young lavas were emplaced at 1-2 Ma, confirming negligible modern bedrock incision. The size of boulders in streams (D84 from gridded point counts and “area-by-area” analysis) covaries with normalized local channel gradient (ksnQ), suggesting that sediment size determines the threshold for motion and that these boulders can block bedrock incision. Finally, catchment-average erosion rates are weakly correlated with MAP, ksnQ and valley wall gradient, suggesting that both fluvial thresholds and sediment flux, modulated by local climate, play a role in setting channel steepness and slowing bedrock incision on the Hawaiian Islands.

Factors affecting the preservation of the isotopic fingerprint of glacial meltwater in mountain groundwater systems

Journal of Hydrology · 2026-01-23

Contrasting weathering behavior of mafic and ultramafic rocks in arc-collision zones

2026-03-14

Consumption of CO2 through weathering of volcanic arc and ophiolite rocks in arc-collision zones in the humid tropics has been proposed to regulate Earth’s climate over geological timescales. Evaluating this hypothesis requires quantifying the factors that control CO2 consumption from weathering of mafic and ultramafic rocks. Temperature, runoff, and physical erosion may each influence weathering rates. To determine their relative importance for arc and ophiolite rocks, we examine co-variation of stream solutes, sediment geochemistry, and erosion rates inferred from cosmogenic 36Cl in magnetite in an ancient, uplifted arc-collision zone in Puerto Rico. The data reveal contrasting weathering behavior between mafic and ultramafic rocks. Consumption of CO2 from mafic rock weathering is primarily limited by the ability of erosion to strip regolith from the landscape. Conversely, ultramafic rock weathering is more strongly controlled by runoff than by erosion. This difference likely results from the low Al concentrations in ultramafic rocks, which inhibit the formation of aluminosilicate clays and thick regolith. Additionally, we find that CO2 consumption is not limited by temperature for either mafic or ultramafic rocks in the tropics. These results have implications for the role of tropical arc-collision zones in the Earth’s negative silicate weathering feedback.

The oldest in situ <i>Homo erectus</i> crania in eastern Asia: The Yunxian site dates to ~1.77 Ma

Science Advances · 2026-02-18 · 1 citations

With the discovery of three almost complete Homo erectus crania, Yunxian is one of the most important early Pleistocene hominin sites in eastern Asia. Yet, the age of the Yunxian fossils has remained debated because of the lack of reliable numerical dating results. Here, we apply the well-established isochron 26 Al/ 10 Be burial dating to quartz gravels from two sediment layers of the site. The age results push the Yunxian crania back to 1.77 ± 0.08 million years ago (±1σ internal error), representing the oldest H. erectus fossils discovered in situ in eastern Asia. A much older age assignment to Yunxian supports the model of rapid dispersal and widespread distribution of early H. erectus and contributes to narrowing the chronological gap between the earliest archaeology and hominin paleontology in eastern Asia.

In situ Produced 10Be and 26Al in Shale Quartz: Structural and Lithologic Influence on Erosion Rates in the Appalachian Valley and Ridge

Abstracts with programs - Geological Society of America · 2025-01-01

Controls of climate and fluvial thresholds on stream incision on the Hawaiian Islands &amp;#160;

2025-03-15

The extent that climate impacts erosion has long been debated and is difficult to decipher, as climate signals are often obscured by tectonic signals. The Hawaiian Islands are excellent settings to test these relationships, as they have no tectonic uplift, well-known base level histories, uniform lithology, and dramatic climate gradients. On Kauai, previous work shows a correlation between rainfall and total canyon incision; however, geologic evidence shows that river incision could not have been constant throughout time: ~2 Ma inset lava flows sit at river level in several canyons on the ~4.5-million-year-old island, indicating that canyon incision has been negligible over the last 2 Myr. One explanation is that boulders and/or sediment flux in streambeds block further incision, acting as thresholds. Channel gradients on the Hawaiian Islands decrease with increasing precipitation and appear to be in equilibrium (uniform ksn below knickpoints), indicating that channel gradient is set by the threshold of boulder or sediment mobility. Therefore, climate appears to be recorded in threshold channel slope and total incision depth instead of time averaged incision rate as previously assumed (Ferrier et al., 2013). We traveled to Kaui and West Maui to test the hypotheses that (a) boulders and/or (b) sediment act as thresholds for fluvial incision, by (a) quantifying channel morphology and boulder size using structure from motion photogrammetry, drone photography and pebble counts, and (b) collecting catchment-average samples for cosmogenic radionuclide analysis (36Cl in magnetite), in catchments across gradients of precipitation rate and channel slope. Preliminary data suggests that boulder size scales with channel gradient within climate zones, indicating that boulders are an important threshold for channel incision. However, if channel gradient is correlated with upcoming denudation rates, sediment flux may be an additional important threshold. Next steps include quantifying basal and critical shear stress for boulder transport and combining data into a landscape evolution model. Ultimately, we aim to answer long-standing questions regarding the roles of climate and fluvial thresholds in landscape evolution, applicable in both tectonically inactive and active landscapes.

Spatiotemporal glacier retreat on the Tibetan Plateau since the LGMG to early holocene based on compilation of moraine boulder ages

Scientific Reports · 2025-01-29 · 4 citations

Tibetan Plateau and its surrounding mountains (TPSM) have experienced prominent glacier retreat since the Global Last Glacial Maximum, while the detailed deglaciation process remains unclear. To investigate the spatiotemporal pattern of the glacier retreat history, we compiled 196 moraines dating from 26.5 to 10 ka based on 994 boulder 10Be exposure age from seven regions on the TPSM and calculated the separated component Gaussians of moraine ages. The result shows that synchronous glacier retreat across the entire TPSM began around 22 ka in response to onset of rising local summer insolation. Moraine abandonment centered at five stages, i.e., 22–20, 19–18 ka, 17–16, 14.5–12.9, and 11.6–10 ka. Synchronous retreat occurred at 22–20 ka and 14.5–12.9 ka in all seven regions, while at 19–18 ka, it occurred in all regions except Tianshan. Pamir and NE Tibet showed no retreat at 17–16 ka, likely due to the sustained influence of the Westerlies. The stage at 11.6–10 ka was absent in Central Tibet due to lack of chronology from the perched moraines therein. This work offers new insights into the evolution of the cryosphere and adjustments in atmospheric circulation on the TPSM.

A 2 m.y. record of bedrock incision and drainage integration of the upper Green River, western United States

Geosphere · 2025-05-13 · 2 citations

Abstract Since the time of John Wesley Powell, integration of the upper Green River (western United States) across the eastern Uinta Mountains has been a subject of great interest and significance for understanding Colorado Plateau evolution. We address the question of the timing of integration by making novel use of detrital sanidine (DS) 40Ar/39Ar geochronology, which, due to the precision of the method, is emerging as an excellent way to constrain terrace ages that are &amp;gt;0.5 Ma in the western United States. The DS dates, in combination with cosmogenic burial and luminescence dates, produced a long-term (~2 m.y.) record of the upper Green River in southwestern Wyoming (USA; Peru Bench) and along the Colorado-Utah, USA, border (Browns Park). DS dating of 3461 sanidine grains from 10 terrace deposits (five from Peru Bench and five from Browns Park) produced maximum depositional ages (MDAs), seven of which show a linear relationship of increasing terrace height and age. The DS MDAs at Peru Bench are: 1.304 ± 0.011 Ma (175 m terrace), 1.020 ± 0.046 Ma (150 m terrace), 0.847 ± 0.009 Ma (125 m terrace), and 0.574 ± 0.045 Ma (75 m terrace). The DS MDAs in Browns Park are: 1.980 ± 0.025 Ma (210 m terrace), 1.283 ± 0.018 Ma (130 m terrace), and 0.670 ± 0.004 Ma (45–60 m terrace). Two cosmogenic burial dates for Peru Bench terraces are: 1.24 ± 0.44 (150 m terrace) and 1.40 ± 0.96 Ma (125 m terrace). Two luminescence dates for Peru Bench terraces are: 59.0 ± 10.4 ka (20–30 m terrace) and 35.4 ± 4.2 ka (5–10 m terrace). Regressions of terrace heights and DS ages from both locations show that long-term bedrock incision rates measured over the past ~2 m.y. have remained remarkably constant through &amp;gt;40 glacial-interglacial cycles, with no apparent influence of the Mid-Pleistocene Transition. This constancy is interpreted to record long-term regional epeirogenic uplift and erosional isostasy. Minimum bedrock incision rates are ~169 m/m.y. at Peru Bench (upstream) and ~114 m/m.y. in Browns Park (downstream). The slower incision rate in Browns Park is interpreted to reflect dampening of incision due to Quaternary subsidence within the Browns Park graben. Stratigraphic relations demonstrate that integration of the upper Green River across the eastern Uinta Mountains occurred after the end of Browns Park Formation sedimentation ca. 8 Ma. Published Colorado River detrital zircon analyses from the Salton Trough suggest that upper Green River integration could have occurred as early as ca. 5 Ma. New DS dates show that upper Green River integration was likely complete by ca. 2 Ma. It is also probable that integration of the upper Green River into the Colorado River system contributed to late Cenozoic exhumation of the Colorado Plateau.

Cave sediment chronology and erosion rates in the São Desidério karst reveal a million-year-scale landscape evolution of the Central Brazilian Plateau

Geomorphology · 2025-05-06

Evolution of denudation during the growth of a thrust-fold range: A case study from the Yumu Shan, NE Tibetan Plateau

Palaeogeography Palaeoclimatology Palaeoecology · 2025-03-23