Charlie Bristow | Birkbeck College, University of London (original) (raw)
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Papers by Charlie Bristow
Research Square (Research Square), Nov 15, 2023
Star dunes are the tallest dunes on Earth and are amongst the largest and most spectacular dynami... more Star dunes are the tallest dunes on Earth and are amongst the largest and most spectacular dynamic landforms. Although they are widespread in modern sandy deserts star dunes are rarely recognised in the rock record probably due to a lack of suitable models. This stratigraphic study of a star dune in the Sahara Desert shows that the dune has developed recently and grown rapidly to create a 100 m high dune within the past thousand years. At the base of the dune there is a period of around eight thousand years that appears to lack sand accumulation, probably due to stabilization of the dunes during the African humid period (AHP). The star dune accumulation postdates the end of the AHP. We present a new model for the structure of a star dune based on a geophysical and geochronological investigation. Individual structural features in star dunes are similar to those from linear or barchanoid dunes, likely leading to misidenti cation in the rock record, but the suite of features we describe will permit identi cation of star dunes in future studies of the rock record.
EGU General Assembly Conference Abstracts, Apr 1, 2015
Ground penetrating radar (GPR) provides almost continuous, high resolution profiles of the shallo... more Ground penetrating radar (GPR) provides almost continuous, high resolution profiles of the shallow subsurface which cannot be achieved by any other geophysical technique. Applications of GPR in geomorphology have increased significantly in recent years due to an increased awareness of the technique, combined with improvements in the equipment which make it more portable, more reliable, and easier to use. The ease of use has presented some problems due to unrealistic expectations, inappropriate survey design, and questionable interpretations. Examples are included to illustrate common ‘problems’ as well as successful GPR surveys.
Engineering and Mining Geophysics 2021
Quaternary Deserts and Climatic Change
Book synopsis: These proceedings record the results of climate change in many areas which are hyp... more Book synopsis: These proceedings record the results of climate change in many areas which are hyper-arid deserts today but which, almost cyclically, at intervals of thousands or even hundreds of thousands of years, have had a much more humid climate
A morpho-geophysical investigation of two beaches in Thailand over the last decade shows that the... more A morpho-geophysical investigation of two beaches in Thailand over the last decade shows that they have completely recovered from the 2004 Indian Ocean tsunami (IOT) without any human intervention. Although the beach systems show contrasting styles of recovery in both cases natural processes have reconstructed the beaches to comparable pre-tsunami morphologies in under a decade, demonstrating the existence of punctuated equilibrium in coastal systems and the resilience of natural systems to catastrophic events. Through a combination of remote sensing, field surveys and shallow geophysics we reconstruct the post-event recovery of beaches at Phra Thong Island, a remote, near pristine site that was severely impacted by the IOT. We identify periods of aggradation, progradation and washover sedimentation that match with local events including a storm in November 2007. The rapid recovery of these systems implies that majority of sediment scoured by the tsunami was not transported far offshore but remained in the littoral zone within reach of fair-weather waves that returned it (the sediment) to the beach naturally.
Sedimentary Geology, 2015
Coastal overwash deposits from tsunamis and storms have been identified and characterised from ma... more Coastal overwash deposits from tsunamis and storms have been identified and characterised from many coastal environments. To date, these investigations have utilised ad-hoc time, energy and cost intensive invasive techniques, such as, pits and trenches or taking core samples. Here, we present the application of high-frequency ground penetrating radar (GPR) to identify and characterise the 2004 Indian Ocean Tsunami (IOT) and palaeotsunami deposits from Phra Thong Island, Thailand. This site is one of the most intensively studied palaeotsunami sites globally and preserves a series of late-Holocene stacked sandy tsunami deposits within an organic, muddy low-energy backbeach environment. Using 100, 500 and 1000 MHz GPR antennas, 29 reflection profiles were collected from two swales (X and Y) inland of the modern beach, and two common mid-point (CMP) profiles using the 200 MHz antennas were collected from Swale Y. Detailed examination of the CMPs allowed accurate velocity estimates to be applied to each profile. The reflection profiles included across-swale profiles and a high-resolution grid in Swale X, and were collected to investigate the feasibility of GPR to image the palaeotsunami deposits, and two profiles from Swale Y where the tsunami deposits are poorly known. The 500 MHz antennas provided the best stratigraphic resolution which was independently validated from the stratigraphy and sedimentology recovered from 17 auger cores collected along the profiles. It is clear from the augers and GPR data, that the different dielectric properties of the individual layers allow the identification of the IOT and earlier tsunami deposits on Phra Thong Island. Although applied in a coastal setting here, this technique can be applied to other environments where thin sand beds are preserved, in order to prioritise sites for detailed examination.
Abstract Palaeolake Megachad had an area of at least 360,000 km2 which is greater than all the Gr... more Abstract Palaeolake Megachad had an area of at least 360,000 km2 which is greater than all the Great Lakes of North America combined. At its peak in it was around 170m deep, 1000 km long and 600 km wide, which would have made it the greatest freshwater lake in Africa. Today Lake Chad is greatly reduced and its northern sub-basin the Bodele Depression is dry. We report the results of optical dating of high-stand beach deposits from around the lake shores in Chad and Nigeria, and the ages of low-stand dune sands preserved within lake ...
Frontiers in Earth Science, 2021
The Gonghe Basin on the Qinghai-Tibet Plateau has a cold, arid climate and has suffered severe la... more The Gonghe Basin on the Qinghai-Tibet Plateau has a cold, arid climate and has suffered severe land degradation. Climate change as well as anthropogenic activities including overgrazing have resulted in widespread blowout development and the formation of some of Earth’s largest blowouts. The blowouts are part of an aeolian dominated landscape that passes from deflation zone to grass covered plain, and then through blowouts of increasing size and complexity to transverse barchanoid dunes that are migrating into the valley of the Yellow River. A combination of structure-from-motion (SfM) optical drone mapping, ground-penetrating radar (GPR) and soil pits are used to investigate blowout scour hollows and depositional lobes. Comparisons of the volumes of sediment removed from the scour hollows with the volumes of sediment deposited within adjacent lobes varies between sites. The lobe volume is invariably less than the volume of the scour hollow. This can, in part, be attributed to aeoli...
Aeolian Geomorphology, 2019
Special Paper 432: Stratigraphic Analyses Using GPR, 2007
... The Turra dune Figure 1. Map of Australia showing the whorl of linear dunes and the location ... more ... The Turra dune Figure 1. Map of Australia showing the whorl of linear dunes and the location of GPR survey sites in the Simpson and Strzelecki deserts. AAlice Springs; BBirdsville; CCamel Flat; D Innamincka. Page 30. 22 Bristow et al. ...
Production of the Namib Sand Sea Digital Database (Livingstone et al. 2010 ) provided a mechanism... more Production of the Namib Sand Sea Digital Database (Livingstone et al. 2010 ) provided a mechanism for identifying recent progress and gaps in understanding of processes and geomorphology within the Namib Sand Sea (see also Livingstone et al. 2014). While remote sensing studies provide coverage of the entire sand sea the majority of field work to date has been at the northern end of the sand sea, usually operating from and using the facilities at the Gobabeb research and Training Centre. We are now extending research across the sand sea, establishing two new meteorological stations in the central and southern Namib Sand Sea. Field work has included GPR and DGPS surveys of the dunes as well as sampling for optical dating in order to test hypotheses on the age and evolution of linear dunes.
Research Square (Research Square), Nov 15, 2023
Star dunes are the tallest dunes on Earth and are amongst the largest and most spectacular dynami... more Star dunes are the tallest dunes on Earth and are amongst the largest and most spectacular dynamic landforms. Although they are widespread in modern sandy deserts star dunes are rarely recognised in the rock record probably due to a lack of suitable models. This stratigraphic study of a star dune in the Sahara Desert shows that the dune has developed recently and grown rapidly to create a 100 m high dune within the past thousand years. At the base of the dune there is a period of around eight thousand years that appears to lack sand accumulation, probably due to stabilization of the dunes during the African humid period (AHP). The star dune accumulation postdates the end of the AHP. We present a new model for the structure of a star dune based on a geophysical and geochronological investigation. Individual structural features in star dunes are similar to those from linear or barchanoid dunes, likely leading to misidenti cation in the rock record, but the suite of features we describe will permit identi cation of star dunes in future studies of the rock record.
EGU General Assembly Conference Abstracts, Apr 1, 2015
Ground penetrating radar (GPR) provides almost continuous, high resolution profiles of the shallo... more Ground penetrating radar (GPR) provides almost continuous, high resolution profiles of the shallow subsurface which cannot be achieved by any other geophysical technique. Applications of GPR in geomorphology have increased significantly in recent years due to an increased awareness of the technique, combined with improvements in the equipment which make it more portable, more reliable, and easier to use. The ease of use has presented some problems due to unrealistic expectations, inappropriate survey design, and questionable interpretations. Examples are included to illustrate common ‘problems’ as well as successful GPR surveys.
Engineering and Mining Geophysics 2021
Quaternary Deserts and Climatic Change
Book synopsis: These proceedings record the results of climate change in many areas which are hyp... more Book synopsis: These proceedings record the results of climate change in many areas which are hyper-arid deserts today but which, almost cyclically, at intervals of thousands or even hundreds of thousands of years, have had a much more humid climate
A morpho-geophysical investigation of two beaches in Thailand over the last decade shows that the... more A morpho-geophysical investigation of two beaches in Thailand over the last decade shows that they have completely recovered from the 2004 Indian Ocean tsunami (IOT) without any human intervention. Although the beach systems show contrasting styles of recovery in both cases natural processes have reconstructed the beaches to comparable pre-tsunami morphologies in under a decade, demonstrating the existence of punctuated equilibrium in coastal systems and the resilience of natural systems to catastrophic events. Through a combination of remote sensing, field surveys and shallow geophysics we reconstruct the post-event recovery of beaches at Phra Thong Island, a remote, near pristine site that was severely impacted by the IOT. We identify periods of aggradation, progradation and washover sedimentation that match with local events including a storm in November 2007. The rapid recovery of these systems implies that majority of sediment scoured by the tsunami was not transported far offshore but remained in the littoral zone within reach of fair-weather waves that returned it (the sediment) to the beach naturally.
Sedimentary Geology, 2015
Coastal overwash deposits from tsunamis and storms have been identified and characterised from ma... more Coastal overwash deposits from tsunamis and storms have been identified and characterised from many coastal environments. To date, these investigations have utilised ad-hoc time, energy and cost intensive invasive techniques, such as, pits and trenches or taking core samples. Here, we present the application of high-frequency ground penetrating radar (GPR) to identify and characterise the 2004 Indian Ocean Tsunami (IOT) and palaeotsunami deposits from Phra Thong Island, Thailand. This site is one of the most intensively studied palaeotsunami sites globally and preserves a series of late-Holocene stacked sandy tsunami deposits within an organic, muddy low-energy backbeach environment. Using 100, 500 and 1000 MHz GPR antennas, 29 reflection profiles were collected from two swales (X and Y) inland of the modern beach, and two common mid-point (CMP) profiles using the 200 MHz antennas were collected from Swale Y. Detailed examination of the CMPs allowed accurate velocity estimates to be applied to each profile. The reflection profiles included across-swale profiles and a high-resolution grid in Swale X, and were collected to investigate the feasibility of GPR to image the palaeotsunami deposits, and two profiles from Swale Y where the tsunami deposits are poorly known. The 500 MHz antennas provided the best stratigraphic resolution which was independently validated from the stratigraphy and sedimentology recovered from 17 auger cores collected along the profiles. It is clear from the augers and GPR data, that the different dielectric properties of the individual layers allow the identification of the IOT and earlier tsunami deposits on Phra Thong Island. Although applied in a coastal setting here, this technique can be applied to other environments where thin sand beds are preserved, in order to prioritise sites for detailed examination.
Abstract Palaeolake Megachad had an area of at least 360,000 km2 which is greater than all the Gr... more Abstract Palaeolake Megachad had an area of at least 360,000 km2 which is greater than all the Great Lakes of North America combined. At its peak in it was around 170m deep, 1000 km long and 600 km wide, which would have made it the greatest freshwater lake in Africa. Today Lake Chad is greatly reduced and its northern sub-basin the Bodele Depression is dry. We report the results of optical dating of high-stand beach deposits from around the lake shores in Chad and Nigeria, and the ages of low-stand dune sands preserved within lake ...
Frontiers in Earth Science, 2021
The Gonghe Basin on the Qinghai-Tibet Plateau has a cold, arid climate and has suffered severe la... more The Gonghe Basin on the Qinghai-Tibet Plateau has a cold, arid climate and has suffered severe land degradation. Climate change as well as anthropogenic activities including overgrazing have resulted in widespread blowout development and the formation of some of Earth’s largest blowouts. The blowouts are part of an aeolian dominated landscape that passes from deflation zone to grass covered plain, and then through blowouts of increasing size and complexity to transverse barchanoid dunes that are migrating into the valley of the Yellow River. A combination of structure-from-motion (SfM) optical drone mapping, ground-penetrating radar (GPR) and soil pits are used to investigate blowout scour hollows and depositional lobes. Comparisons of the volumes of sediment removed from the scour hollows with the volumes of sediment deposited within adjacent lobes varies between sites. The lobe volume is invariably less than the volume of the scour hollow. This can, in part, be attributed to aeoli...
Aeolian Geomorphology, 2019
Special Paper 432: Stratigraphic Analyses Using GPR, 2007
... The Turra dune Figure 1. Map of Australia showing the whorl of linear dunes and the location ... more ... The Turra dune Figure 1. Map of Australia showing the whorl of linear dunes and the location of GPR survey sites in the Simpson and Strzelecki deserts. AAlice Springs; BBirdsville; CCamel Flat; D Innamincka. Page 30. 22 Bristow et al. ...
Production of the Namib Sand Sea Digital Database (Livingstone et al. 2010 ) provided a mechanism... more Production of the Namib Sand Sea Digital Database (Livingstone et al. 2010 ) provided a mechanism for identifying recent progress and gaps in understanding of processes and geomorphology within the Namib Sand Sea (see also Livingstone et al. 2014). While remote sensing studies provide coverage of the entire sand sea the majority of field work to date has been at the northern end of the sand sea, usually operating from and using the facilities at the Gobabeb research and Training Centre. We are now extending research across the sand sea, establishing two new meteorological stations in the central and southern Namib Sand Sea. Field work has included GPR and DGPS surveys of the dunes as well as sampling for optical dating in order to test hypotheses on the age and evolution of linear dunes.