Streamlined islands and the English Channel megaflood hypothesis

Collier, Jenny; Oggioni, Francesca; Gupta, Sanjeev; García-Moreno, D.; Trentesaux, Alain; Batist, Marc De

doi:10.1016/j.gloplacha.2015.11.004

Cited by 27 publications

(43 citation statements)

References 68 publications

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“…1) shows that a prominent valley, the Lobourg Channel71330, in the Dover Strait can be traced southwestwards into a network of bedrock-eroded valleys in the central Channel57. Individual valleys, such as the Northern Palaeovalley, have an anabranching planform morphology with channels bifurcating around streamlined bedrock remnants57. The continuity of the valley network, in particular the Northern Palaeovalley, with the Lobourg Channel in the Dover Strait establishes them as part of the same palaeodrainage system7 (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Individual valleys, such as the Northern Palaeovalley, have an anabranching planform morphology with channels bifurcating around streamlined bedrock remnants57. The continuity of the valley network, in particular the Northern Palaeovalley, with the Lobourg Channel in the Dover Strait establishes them as part of the same palaeodrainage system7 (Fig. 2).…”

Section: Resultsmentioning

confidence: 99%

“…It is widely considered that the breaching of the chalk ridge and opening of the Dover Strait is a consequence of spillover of a proglacial lake that occupied the present-day Southern North Sea basin during the Marine Isotope Stage (MIS) 12 glaciation (∼450 ka and conventionally equated to the Elsterian–Anglian glaciation)34567. Coalescence of the British and Scandinavian ice sheets in the northern and central North Sea basin and the chalk barrier to the south caused fluvial discharge from European rivers and glacial meltwater to become ponded to form this lake26.…”

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“…Lake spillover is thought to have released a significant megaflood into a subaerial English Channel45. An extensive network of bedrock-eroded valleys48910 in the central English Channel shows morphologies characteristic of erosion by high magnitude flood flows57, and has been interpreted as a consequence of catastrophic drainage of a pro-glacial lake57. Others contend that while a proglacial lake existed in the southern North Sea, its spillover was not a catastrophic process11.…”

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confidence: 99%

“…In this model, there is no requirement for a proglacial lake in the southern North Sea basin. Thus models for erosion of the palaeovalley networks downstream of the Dover Strait range from those proposing erosion by high-magnitude events57 to those suggesting relatively slow fluvial erosion13. Testing of models for opening of the Strait has, however, been limited through lack of high-resolution marine geophysical data at the inferred breach point in the Dover Strait.…”

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Two-stage opening of the Dover Strait and the origin of island Britain

et al. 2017

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Late Quaternary separation of Britain from mainland Europe is considered to be a consequence of spillover of a large proglacial lake in the Southern North Sea basin. Lake spillover is inferred to have caused breaching of a rock ridge at the Dover Strait, although this hypothesis remains untested. Here we show that opening of the Strait involved at least two major episodes of erosion. Sub-bottom records reveal a remarkable set of sediment-infilled depressions that are deeply incised into bedrock that we interpret as giant plunge pools. These support a model of initial erosion of the Dover Strait by lake overspill, plunge pool erosion by waterfalls and subsequent dam breaching. Cross-cutting of these landforms by a prominent bedrock-eroded valley that is characterized by features associated with catastrophic flooding indicates final breaching of the Strait by high-magnitude flows. These events set-up conditions for island Britain during sea-level highstands and caused large-scale re-routing of NW European drainage.

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confidence: 99%

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Two-stage opening of the Dover Strait and the origin of island Britain

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Amazonian fluvial outflow channels in Jovis Tholus region, Mars

Vijayan

Sinha

2017

JGR Planets

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Outflow channels are prevalent on the surface of Mars, and they are one of the strongest lines of evidence for fluvial activity. The purported presence of some of the channel networks on the Amazonian surface provides evidence for recent surficial fluvial activity. We describe morphological evidence collectively diagnostic of fluvial origin for the channels located northwest (NW) of Jovis Tholus, within the Tharsis volcanic province. The fluvial relationships are deciphered from (1) morphological analysis of catastrophic effusion associated with the graben system superposed over the NW portion of an unnamed crater ejecta (19.85°N, 118.03°W) and (2) crater‐size frequency distributions of unnamed crater ejecta revealing the tentative period of the fluvial activity. Channels, streamlined/curvilinear islands, terraces, divide crossing, crossover channels, networks of braided‐like channels, and eroded ejecta are collectively suggestive of fluvial outflow that emanated from the graben. Chronological analysis revealed that the unnamed crater formed at ~3.4 Ga. Subsequently, the NW part of crater ejecta was incised by a channel network originated from the graben. Furthermore, we infer that the current channel floor has undergone volcanic and aeolian resurfacing to some extent, and the estimated modeled resurfaced channel age is ~0.2–0.5 Ga. This reveals that the fluvial activity possibly occurred after the crater formation, but before channel floor resurfacing, which is during Early to Middle Amazonian. Nevertheless, the potential source for the channel formation likely persisted under this region since the pre‐Amazonian epoch. The suite of these fluvial features inferred within the Jovis Tholus region outflow channel system thus adds one another evidence for Amazonian fluvial activity.

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New insights into the Quaternary evolution of the Bristol Channel, UK

Gibbard

Hughes

Rolfe

2017

J Quaternary Science

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A synthesis of new publically available borehole and bathymetric data, combined with a wealth of other existing disparate data sources, reveals new insights into the Quaternary history of the Bristol Channel area. Sediment boreholes throughout the Bristol Channel confirm the area was glaciated in the Pleistocene. Till is present below marine deposits and, in some areas, is visible morphologically as submerged moraines. In the central and eastern Bristol Channel the submerged valley course of the palaeo‐Severn is very clear in new high‐resolution bathymetric surveys. This former river course and associated tributaries cross‐cut through glacial sediments in the Bristol Channel. At least three phases of glaciation are recorded in the Bristol Channel, one related to the southern limits of a Late Devensian Substage (∼Marine Isotope Stage (MIS) 2) Welsh Ice Cap which reached into Swansea Bay, an earlier Devensian (MIS 4–3) glaciation associated with Irish Sea ice, and another older glaciation that is associated with ice that filled the entire outer and central Bristol Channel. The age of the older Bristol Channel glaciation is still open, although it pre‐dates the Devensian (Late Pleistocene) and must date to the Middle Pleistocene. It is therefore evident that Pleistocene glacial and fluvial activity, combined with subsequent post‐glacial sea transgression, directly account for current morphometries of the Bristol Channel and Severn Estuary, and the current geography of the SW British Isles.

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Streamlined islands and the English Channel megaflood hypothesis

Cited by 27 publications

References 68 publications

Two-stage opening of the Dover Strait and the origin of island Britain

Two-stage opening of the Dover Strait and the origin of island Britain

Amazonian fluvial outflow channels in Jovis Tholus region, Mars

New insights into the Quaternary evolution of the Bristol Channel, UK

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