scholarly journals Short communication: Forward and inverse models relating river long profile to monotonic step-changes in tectonic rock uplift rate history: A theoretical perspective under a nonlinear slope-erosion dependency

2021 ◽  
Author(s):  
Yizhou Wang ◽  
Liran Goren ◽  
Dewen Zheng ◽  
Huiping Zhang
Keyword(s):  
Theoretical Perspective ◽  
Tectonic Uplift ◽  
Analytic Model ◽  
Uplift Rate ◽  
Channel Dynamics ◽  
Tectonic History ◽  
Inverse Models ◽  
Before And After ◽  
Uplift Rates ◽  
River Profiles

Abstract. The long profile of rivers is widely considered as a recorded of tectonic uplift rate. Knickpoints form in response to rate changes and faster rates produce steeper channel segments. However, when the exponent relating fluvial incision to river slope, n, is not unity, the links between tectonic rates and channel profile are complicated by channel dynamics that consume and form river segments. Here, we explore non-linear cases leading to channel segment consumption and develop a Lagrangian analytic model for knickpoint migration. We derive a criterion for knickpoint preservation and merging, and develop a forward analytic model that resolves knickpoint and long profile evolution before and after knickpoint merging. We further propose a linear inverse scheme to infer tectonic history from river profiles when all knickpoints are preserved. Our description provides a new framework to explore the links between tectonic uplift rates and river profile evolution when n is not unity.

scholarly journals Dynamics of Erosion and Deposition in a Partially Restored Valley-Bottom Gully

Land ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 62
Author(s):  
Alberto Alfonso-Torreño ◽  
Álvaro Gómez-Gutiérrez ◽  
Susanne Schnabel
Keyword(s):  
High Resolution ◽  
Sediment Deposition ◽  
Aerial Images ◽  
Valley Bottom ◽  
Erosion And Deposition ◽  
Channel Dynamics ◽  
Check Dams ◽  
Before And After ◽  
Multi Temporal ◽  
Spatio Temporal

Gullies are sources and reservoirs of sediments and perform as efficient transfers of runoff and sediments. In recent years, several techniques and technologies emerged to facilitate monitoring of gully dynamics at unprecedented spatial and temporal resolutions. Here we present a detailed study of a valley-bottom gully in a Mediterranean rangeland with a savannah-like vegetation cover that was partially restored in 2017. Restoration activities included check dams (gabion weirs and fascines) and livestock exclosure by fencing. The specific objectives of this work were: (1) to analyze the effectiveness of the restoration activities, (2) to study erosion and deposition dynamics before and after the restoration activities using high-resolution digital elevation models (DEMs), (3) to examine the role of micro-morphology on the observed topographic changes, and (4) to compare the current and recent channel dynamics with previous studies conducted in the same study area through different methods and spatio-temporal scales, quantifying medium-term changes. Topographic changes were estimated using multi-temporal, high-resolution DEMs produced using structure-from-motion (SfM) photogrammetry and aerial images acquired by a fixed-wing unmanned aerial vehicle (UAV). The performance of the restoration activities was satisfactory to control gully erosion. Check dams were effective favoring sediment deposition and reducing lateral bank erosion. Livestock exclosure promoted the stabilization of bank headcuts. The implemented restoration measures increased notably sediment deposition.

Formation and preservation of marine terraces during multiple sea level stands

2021 ◽  
Author(s):  
Luca C Malatesta ◽  
Noah J. Finnegan ◽  
Kimberly Huppert ◽  
Emily Carreño
Keyword(s):  
Sea Level ◽  
Basic Assumption ◽  
Cumulative Exposure ◽  
Marine Terrace ◽  
Uplift Rate ◽  
Marine Terraces ◽  
Uplift Rates ◽  
Ca 50 ◽  
Wave Erosion ◽  
Mis 5E

<p>Marine terraces are a cornerstone for the study of paleo sea level and crustal deformation. Commonly, individual erosive marine terraces are attributed to unique sea level high-stands. This stems from early reasoning that marine platforms could only be significantly widened under moderate rates of sea level rise as at the beginning of an interglacial and preserved onshore by subsequent sea level fall. However, if marine terraces are only created during brief windows at the start of interglacials, this implies that terraces are unchanged over the vast majority of their evolution, despite an often complex submergence history during which waves are constantly acting on the coastline, regardless of the sea level stand.<span> </span></p><p>Here, we question the basic assumption that individual marine terraces are uniquely linked to distinct sea level high stands and highlight how a single marine terrace can be created By reoccupation of the same uplifting platform by successive sea level stands. We then identify the biases that such polygenetic terraces can introduce into relative sea level reconstructions and inferences of rock uplift rates from marine terrace chronostratigraphy.</p><p>Over time, a terrace’s cumulative exposure to wave erosion depends on the local rock uplift rate. Faster rock uplift rates lead to less frequent (fewer reoccupations) or even single episodes of wave erosion of an uplifting terrace and the generation and preservation of numerous terraces. Whereas slower rock uplift rates lead to repeated erosion of a smaller number of polygenetic terraces. The frequency and duration of terrace exposure to wave erosion at sea level depend strongly on rock uplift rate.</p><p>Certain rock uplift rates may therefore promote the generation and preservation of particular terraces (e.g. those eroded during recent interglacials). For example, under a rock uplift rate of ca. 1.2 mm/yr, Marine Isotope Stage (MIS) 5e (ca. 120 ka) would resubmerge a terrace eroded ca. 50 kyr earlier for tens of kyr during MIS 6d–e stages (ca. 190–170 ka) and expose it to further wave erosion at sea level. This reoccupation could accordingly promote the formation of a particularly wide or well planed terrace associated with MIS 5e with a greater chance of being preserved and identified. This effect is potentially illustrated by a global compilation of rock uplift rates derived from MIS 5e terraces. It shows an unusual abundance of marine terraces documenting uplift rates between 0.8 and 1.2 mm/yr, supporting the hypothesis that these uplift rates promote exposure of the same terrace to wave erosion during multiple sea level stands.</p><p>Hence, the elevations and widths of terraces eroded during specific sea level stands vary widely from site-to-site and depend on local rock uplift rate. Terraces do not necessarily correspond to an elevation close to that of the latest sea level high-stand but may reflect the elevation of an older, longer-lived, occupation. This leads to potential misidentification of terraces if each terrace in a sequence is assumed to form uniquely at successive interglacial high stands and to reflect their elevations.</p>

scholarly journals Towards assessing the influence of sediment loading on Last Interglacial sea level

2019 ◽  
Vol 220 (1) ◽  
pp. 384-392
Author(s):  
T Pico
Keyword(s):  
Sea Level ◽  
Tectonic Uplift ◽  
Sediment Loading ◽  
Glacial Cycle ◽  
Last Interglacial ◽  
Isostatic Adjustment ◽  
Uplift Rates ◽  
History Of ◽  
The Impact ◽  
The Last Glacial

SUMMARY Locally, the elevation of last interglacial (LIG; ∼122 ka) sea level markers is modulated by processes of vertical displacement, such as tectonic uplift or glacial isostatic adjustment, and these processes must be accounted for in deriving estimates of global ice volumes from geological sea level records. The impact of sediment loading on LIG sea level markers is generally not accounted for in these corrections, as it is assumed that the impact is negligible except in extremely high depositional settings, such as the world's largest river deltas. Here we perform a generalized test to assess the extent to which sediment loading may impact global variability in the present-day elevation of LIG sea level markers. We numerically simulate river sediment deposition using a diffusive model that incorporates a migrating shoreline to construct a global history of sedimentation over the last glacial cycle. We then calculate sea level changes due to this sediment loading using a gravitationally self-consistent model of glacial isostatic adjustment, and compare these predictions to a global compilation of LIG sea level data. We perform a statistical analysis, which accounts for spatial autocorrelation, across a global compilation of 1287 LIG sea level markers. Though limited by uncertainties in the LIG sea level database and the precise history of river deposition, this analysis suggests there is not a statistically significant global signal of sediment loading in LIG sea level markers. Nevertheless, at sites where LIG sea level markers have been measured, local sea level predicted using our simulated sediment loading history is perturbed up to 16 m. More generally, these predictions establish the relative sensitivity of different regions to sediment loading. Finally, we consider the implications of our results for estimates of tectonic uplift rates derived from LIG marine terraces; we predict that sediment loading causes 5–10 m of subsidence over the last glacial cycle at specific locations along active margin regions such as California and Barbados, where deriving long-term tectonic uplift rates from LIG shorelines is a common practice.

scholarly journals Dating and morpho-stratigraphy of uplifted marine terraces in the Makran subduction zone (Iran)

2019 ◽  
Vol 7 (1) ◽  
pp. 321-344 ◽  
Author(s):  
Raphaël Normand ◽  
Guy Simpson ◽  
Frédéric Herman ◽  
Rabiul Haque Biswas ◽  
Abbas Bahroudi ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Active Surface ◽  
Optically Stimulated Luminescence ◽  
Uplift Rate ◽  
Makran Subduction Zone ◽  
Megathrust Earthquakes ◽  
Surface Uplift ◽  
Marine Terraces ◽  
Uplift Rates ◽  
East West

Abstract. The western part of the Makran subduction zone (Iran) is currently experiencing active surface uplift, as attested by the presence of emerged marine terraces along the coast. To better understand the uplift recorded by these terraces, we investigated seven localities along the Iranian Makran and we performed radiocarbon, 230Th∕U and optically stimulated luminescence (OSL) dating of the layers of marine sediments deposited on top of the terraces. This enabled us to correlate the terraces regionally and to assign them to different Quaternary sea-level highstands. Our results show east–west variations in surface uplift rates mostly between 0.05 and 1.2 mm yr−1. We detected a region of anomalously high uplift rate, where two MIS 3 terraces are emerged, but we are uncertain how to interpret these results in a geologically coherent context. Although it is presently not clear whether the uplift of the terraces is linked to the occurrence of large megathrust earthquakes, our results highlight rapid surface uplift for a subduction zone context and heterogeneous accumulation of deformation in the overriding plate.

Divide mobility controls knickpoint migration on the Roan Plateau

2020 ◽  
Author(s):  
Wolfgang Schwanghart ◽  
Dirk Scherler
Keyword(s):  
Colorado River ◽  
Drainage Area ◽  
Lagrangian Model ◽  
Drainage Network ◽  
Migration Rates ◽  
Tectonic History ◽  
Area Loss ◽  
Temporal Aspects ◽  
History Of ◽  
River Profiles

<p>Knickpoints in longitudinal river profiles provide proxies for the climatic and tectonic history of active mountains. The analysis of river profiles commonly relies on the assumption that drainage network configurations are stable. Here we show that this assumption must made cautiously if changes in contributing area are fast relative to knickpoint migration rates. We study the Parachute Creek basin in the Roan Plateau, Colorado, United States. Low spatial variations in climate and erosional efficiency permit us to reveal and quantify drainage-area loss that occurred in one of the subbasins where observed knickpoint locations are farther upstream than predicted by a model that takes present-day drainage areas into account. We developed a Lagrangian model of knickpoint migration which enables us to study the kinematic links between drainage area loss and knickpoint migration and that provides us with constraints on the temporal aspects of area loss. Modelled onset and amount of area loss are consistent with cliff retreat rates along the margin of the Roan Plateau inferred from the incisional history of the upper Colorado River.</p>

River profiles from digital elevation models – limitations and new ideas

2020 ◽  
Author(s):  
Stefan Hergarten ◽  
Jörg Robl
Keyword(s):  
Tectonic Geomorphology ◽  
Limiting Factor ◽  
Mesh Width ◽  
Tectonic History ◽  
Digital Elevation ◽  
New Ideas ◽  
Channel Slope ◽  
River Profiles ◽  
Made In

<p>Longitudinal river profiles have been a central if not even the most important subject in tectonic geomorphology since the 1950s. During the last decades, considerable progress has been made in unraveling the tectonic history from river profiles. Going along with the rapidly increasing availability of DEMs, however, scientists try to derive more and more information from the topography. So the quality of the DEM is still a limiting factor in many studies. In particular, local channel slopes are strongly affected by the DEM. Several approaches have been proposed in order to reduce the errors and to distinguish specific features such as knickpoints from noise of the DEM.</p><p>In this study we use DEMs with a mesh width of 1 m obtained from airborne laser scans and reduce their resolution artificially in order to analyze the effect of the mesh width on the accuracy of river profiles systematically. Based on the results, we present an idea how the errors in channel slope could be reduced with focus on narrow valleys. Going beyond the majority of the previously published approaches, our idea does not only take into account the elevation along the river profile, but also the curvature of the topography in direction normal to the valley floor.</p><p> </p>

scholarly journals KECEPATAN PENGANGKATAN PULAU BUTON DAN JEJAK PERUBAHANMUKA AIR LAUT DI ZAMAN KUARTER

2016 ◽  
Vol 1 (2) ◽  
Author(s):  
Prijantono Astjario ◽  
D.A. Siregar
Keyword(s):  
Sea Level ◽  
Radiocarbon Dating ◽  
Active Fault ◽  
Present Situation ◽  
Tectonic Uplift ◽  
The Other ◽  
Uplift Rate ◽  
Sea Level Fluctuations ◽  
Astronomical Theory ◽  
Reef Platform

Beberapa indikasi menunjukan adanya jejak muka laut cukup tinggi di zaman Kuarter, ketinggiannya mencapai ±250 meter diatas muka laut masa kini, ditemukan pada kawasan pantai Tira hingga Tanjung Labokeh, Buton bagian selatan. Jejak tersebut terrekam pada permukaan terumbu karang yang membentuk undak laut di kawasan pantai Buton Selatan. Tujuh buah hasil pentarikhkan Radiokarbon memberikan tiga contoh berumur 1500 hingga 3000 tahun dan contoh terumbu karang lainnya berumur lebih tua dari 40.000 tahun sebelum saat ini. Runtunan data Radiokarbon secara garis besar menunjukan kesesuaian dengan perubahan muka laut pada zaman Kuarter yang telah di prakirakan oleh teori astronomi perubahan cuaca masa lalu. Jika dibandingkan data Radiokarvbon dengan data urutan undak laut menunjukan bahwa rata-rata aktivitas tektonik pengangkatan dikawasan pantai Tira hingga Tanjung Labokeh adalah 0,7 = 0,8 mm/tahun. Pengangkatan rata-rata Pulau Buton tampak lebih cepat dari Pulau Muna akibat adanya sesar aktiv diantara kedua pulau tersebut. Several indicators of a slightly higher Quaternary sea-level, reaching about ± 250 meters above the present situation have been found along the coastas of Tira to Cape Labokeh. South Buton. They are corrals in growth position on the surface of reef platform of South Buton. Seven Radiocarbbon datings have provided ages of three samplewsa are 1500 to 3000 and the other four samples are more older than 40.000 years BP. The Radiochronological data are thus broadly consistent with the timing of sea-level fluctuations predicted by the astronomical theory of paleoclimates. Comparision with the data from terraces sequences and from Radiocarbon dating records indicates that the average tectonic uplift rate at Tira and Cape Labokeh, South Buton is on the order of 0,7 – 0.8 mm / years. The uplift rate of Buton is more faster than Muna because of the active fault in between.

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