Some Geomorphic Features of Central Peninsular Florida

10.35256/b41 ◽  
1958 ◽  
Keyword(s):  
Geomorphic Features

Rock varnish record of the African Humid Period in the Lake Turkana basin of East Africa

The Holocene ◽  
2021 ◽  
pp. 095968362110116
Author(s):  
Tanzhuo Liu ◽  
Christopher J Lepre ◽  
Sidney R Hemming ◽  
Wallace S Broecker
Keyword(s):  
East Africa ◽  
Lake Level ◽  
Drainage System ◽  
Early Holocene ◽  
Lake Turkana ◽  
Moisture Condition ◽  
Turkana Basin ◽  
Rock Varnish ◽  
Geomorphic Features ◽  
Humid Period

Rock varnish is a manganiferous dark coating accreted on subaerially exposed rocks in drylands. It often contains a layered microstratigraphy that records past wetness variations. Varnish samples from latest Pleistocene and Holocene geomorphic features in the Lake Turkana basin, East Africa display a regionally replicable microstratigraphy record of Holocene millennial-scale wetness variability and a broad interval of wetter conditions during the African Humid Period (AHP). Three major wet pulses in the varnish record occurred during the generally wet interval of the early Holocene (11.5–8.5 ka) when the lake attained its maximum high stand (MHS) at 455–460 m. A >23 m drop from the MHS occurred between 8.5 and 8 ka. Subsequently two additional wet pulses occurred during the early to middle Holocene (8–5 ka) when the lake occupied its secondary high stand at 445 m. Collectively, these five wet phases represent an extended wet interval coincident with the AHP in the region. One moderate wet phase occurred during the subsequent climatic transition from the humid to arid regime (5–4.3 ka) after the lake level dropped rapidly from 445 m to <405 m. Five minor wet phases took place during the overall arid period of the late Holocene (4.3–0 ka) when the lake level oscillated below 405 m. These findings indicate that the AHP terminated rapidly around 5 ka in the Turkana basin in terms of lake level drop, but the regional shift in relative humidity from the AHP mode to its present-day condition lagged for about 700 years until 4.3 ka, hinting at a gradual phasing out in terms of moisture condition. These findings further suggest that Lake Turkana overflowed intermittently into the Nile drainage system through its topographic sill at 455–460 m during the early Holocene and has become a closed-basin lake thereafter for the past 8 ky.

scholarly journals Applying floodplain geomorphology to flood management (The Lower Vistula River upstream from Plock, Poland)

2020 ◽  
Vol 12 (1) ◽  
pp. 1003-1016
Author(s):  
Grzegorz Wierzbicki ◽  
Piotr Ostrowski ◽  
Tomasz Falkowski
Keyword(s):  
Flood Hazard ◽  
Field Work ◽  
Flood Management ◽  
Erosion And Deposition ◽  
Geomorphological Mapping ◽  
Vistula River ◽  
Overbank Flow ◽  
Geomorphic Features ◽  
Gradient Condition ◽  
Topographical Maps

AbstractUsing remote sensing extended on geological and topographical maps and verified by the field work, we present the flood management and study the geomorphic features of the floodplain of a large, sand bed, untrained but embanked river in order to determine the flood hazard and to predict future flood scenarios. In geomorphological mapping, we focus on the landforms: crevasse channels and splays, flood basin, chute channels, side arms, floodplain channels, dunes and fields of aeolian sand. We base the flood risk assessment on consultations with environmental engineers who design new technical structures that control inundation (cut-off walls and lattice levees). We describe a levee breach as a result of piping (inner erosion) in a high hydraulic gradient condition and its effect (scour hole) as an erosional landform consistent with the repetitive pattern of erosion and deposition formed by an overbank flow on a floodplain. We reveal an existence of homogenous morphodynamic reaches in the river valley.

Geomorphic features and benthic habitats of a subarctic fjard: Okak Bay, Nunatsiavut, Labrador

2020 ◽  
pp. 303-317
Author(s):  
Mallory Carpenter ◽  
Tanya M Brown ◽  
Trevor Bell ◽  
André Martel ◽  
Evan Edinger
Keyword(s):  
Benthic Habitats ◽  
Geomorphic Features

Possible new evidence for Mid-Pleistocene glaciation in the Vale of Pickering, North Yorkshire, UK

2021 ◽  
pp. pygs2020-019
Author(s):  
William A. Fairburn ◽  
Mark D. Bateman
Keyword(s):  
Ice Sheet ◽  
Luminescence Dating ◽  
Marine Isotope Stage ◽  
Pleistocene Glaciation ◽  
Infra Red ◽  
Geomorphic Features ◽  
Ice Field ◽  
Sand And Gravel ◽  
New Evidence ◽  
Stimulation Of

Whilst the Late Devensian glaciation (MIS2) of the Vale of Pickering is well-documented, earlier glaciations within it are not. A proposed limited glaciation in the Mid-Pleistocene, thought to be of Marine Isotope Stage 8 (MIS) age is not well constrained. This paper aimed to obtain preliminary ages for two of the most prominent geomorphic features in the Vale of Pickering to see if they related to pre-Devensian glaciations. New luminescence dating by infra-red stimulation of feldspars from sand accumulations near the summit of Gallows Hill, part of the Wykeham Moraine, and from a section through poorly sorted fluvial sand and gravel on the flanks of the Hutton Buscel Terrace in Yedman Dale gave ages of 176±14 ka and 156±12 ka respectively. Evidence suggests they represent a glacial incursion (MIS 6) into the Vale of Pickering blocking its eastern end and forming a pre-Devensian Glacial Lake Pickering. Whilst they could be older, this style of glaciation is very different to the limited plateau ice-field proposed for MIS 8 at the western end of the Vale of Pickering. Taken at face value, these preliminary ages suggest that the Vale of Pickering was partially glaciated in MIS 6 as part of a wider ice-sheet and contemporary with the Saalian glaciation in Europe.

scholarly journals Experimental migration of knickpoints: influence of style of base-level fall and bed lithology

2016 ◽  
Vol 4 (1) ◽  
pp. 11-23 ◽  
Author(s):  
J.-L. Grimaud ◽  
C. Paola ◽  
V. Voller
Keyword(s):  
Fall Rate ◽  
Pool Depth ◽  
Similar Shape ◽  
Base Level ◽  
Self Organized ◽  
Plunge Pool ◽  
Source To Sink ◽  
Constant Rate ◽  
Geomorphic Features ◽  
River Profiles

Abstract. Knickpoints are fascinating and common geomorphic features whose dynamics influence the development of landscapes and source-to-sink systems – in particular the upstream propagation of erosion. Here, we study river profiles and associated knickpoints experimentally in a microflume filled with a cohesive substrate made of silica, water and kaolinite. We focus on the effect on knickpoint dynamics of varying the distribution of base-level fall (rate, increment, and period) and substrate strength, i.e., kaolinite content. Such simple cases are directly comparable to both bedrock and alluvial river systems. Under a constant rate of base-level fall, knickpoints of similar shape are periodically generated, highlighting self-organized dynamics in which steady forcing leads to multiple knickpoint events. Temporary shielding of the bed by alluvium controls the spacing between these unit knickpoints. Shielding is, however, not effective when base-level drops exceed alluvium thickness. While the base-level fall rate controls the overall slope of experiments, it is not instrumental in dictating the major characteristics of unit knickpoints. Instead the velocity, face slope and associated plunge pool depth of these knickpoints are all strongly influenced by lithology. The period between knickpoints is set by both alluvium thickness and base-level fall rate, allowing use of knickpoint spacing along rivers as an indicator of base-level fall rate.

Influence of wildfire severity on geomorphic features and riparian vegetation of forested streams of the Sierra Nevada, California, USA

2020 ◽  
Vol 29 (7) ◽  
pp. 611
Author(s):  
Breeanne K. Jackson ◽  
S. Mažeika P. Sullivan
Keyword(s):  
Sierra Nevada ◽  
Riparian Vegetation ◽  
Fire Severity ◽  
Riparian Ecosystems ◽  
High Severity ◽  
Sediment Size ◽  
Rim Fire ◽  
Geomorphic Features ◽  
Biodiversity And Ecosystem Function ◽  
Riparian Plant

Fires are a common feature of many landscapes, with numerous and complex ecological consequences. In stream ecosystems, fire can strongly influence fluvial geomorphic characteristics and riparian vegetation, which are structural components of stream–riparian ecosystems that contribute to biodiversity and ecosystem function. However, the effects of fire severity on stream–riparian ecosystems in California’s Sierra Nevada region (USA) are not well described, yet critical for effectively informing fire management and policy. At 12 stream reaches paired by fire severity (one high-severity burned, one low-severity burned), no significant differences were found in riparian plant community cover and composition or stream geomorphic characteristics 2–15 years following wildfire. In addition, minimal changes in riparian vegetation and stream geomorphic properties were observed in the first summer following the extensive and severe Rim Fire. However, an upstream-to-downstream influence of multiple fire occurrences was observed over the previous 81 years within each catchment on stream geomorphic metrics, including sediment size, embeddedness and channel geometry, at our study reaches. The inconsistent effects of wildfire on stream–riparian vegetation and geomorphic characteristics over space and time may be related to time since fire and precipitation.

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