Talk:Goring Gap

Comment by Sandvika

I'm sceptical about the claim but then turned northeast to flow through Hertfordshire before eventually reaching the North Sea in East Anglia near Ipswich.

What should be detailed here is the original course of the river, pre-glaciation. Where did it flow?

It is reasonable to believe that it flowed to the north of the Chiltern/Wessex Downs escarpment, since there was no way through, before the Goring Gap, but what evidence is there for this? The present topology is of River Thame flowing from Aylesbury to Thame - the opposite direction. Perhaps "Lake Oxford" existed as a substantial body of water between the run-off from the Cotswolds and the Chiltern escarpment?

Perhaps this drained eastward over what is now the source of the Thame towards Pitstone (~100m altitude), then Leighton buzzard, joining the Ouzel, then the Great Ouse and reaching the North Sea at Kings Lynn? This would seems plausible, taking account of the topology of the Chilterns and current watershed. The Grand Union Canal has a summit section at Tring (~125m altitude), northwards (and downhill) it follows the Ouzel. It does not seem reasonable that the Thames should "climb" 25m over Tring summit then descend into the Vale of St. Albans, let alone find a route across East Anglia to Ipswich. Thus, I would contest the notion that it flowed through Hertfordshire.

Perhaps Lake Oxford drained westward over what is now the source of the Ray near Swindon (~100m altitude), then Wootton Bassett, joining the Avon entering the Severn at Avonmouth?

In any event, before the Goring Gap, the lowest egress was ~100m altitude so Lake Oxford would have extended west to Swindon, east to Aylesbury and north to Banbury. Huge indeed!

I would suggest that the estuary of the Great Ouse, namely The Wash, looks more the part for a mighty river, "the old Thames", than the more diminuitive Avonmouth.

During the glaciation, it is of course understood that any such northerly course would be obstructed and a new more southerly route found. If Lake Oxford's north-eastern outflow was blocked by ice, then conceivably the water level could have increased to the point where it overflowed at Tring, however this would have followed a southerly route such as the current River Bulbourne via Berkhamsted, then Gade, Colne, still draining into what is the current lower Thames Valley, not across East Anglia to Ipswich. However, the supposition must be that any such egress, if it existed, was also obstructed by ice such that the breach at Goring occurred, leading to the formation of the Goring Gap. —Preceding unsigned comment added by Sandvika (talk • contribs) 00:25, 6 February 2009 (UTC)

Formation of Goring Gap

The paragraph on the formation is highly inaccurate. A great deal is known about the route of the Thames over the last half million years (see many works by Dave Bridgland and Phil Gibbard and others; also the BGS maps of Reading, Henley and Beaconsfield) and none of it involves a Lake Oxford, which never existed. There are no lake sediments upstream of the Gap, but there are well-documented river terrace deposits e.g the Summertown-Radley terrace. The Thames was indeed glacially diverted from its ancestral course, but it did not run north of the Chilterns; it ran northeast from the Reading area (i.e. had already passed through the Gap) to meet the North Sea in Suffolk/Norfolk. The course through what is now Watford was blocked by a tongue of ice during the Anglian glaciation ~ 450 ka, resulting in a proglacial lake and fan deposits north of Slough, and the sudden southward bend of the Thames at Cookham when the lake overflowed and took over what had been the valley of the Kennet. The BGS map of Beaconsfield 255 shows a good map of this. The origin of the Gap is rather simpler. We know the course of the pre-Anglian Thames downstream of the gap, and the highest reliable terrace currently lies at around 110 m OD, whereas the current crest of the Chilterns/Berkshire Downs ridge near the Gap is only some 30 m higher than that - in other words it ran in a shallow valley similar to the modern Thames. The reason for the elevation difference is that the whole area has been progressively uplifted during the last few hundred thoudsand years, mostly as a result of the removal of mass by heavyweight erosion during glacial periods and the consequent isostatic rise. The uplift may have been of the order of 90 m in this area, such that the ancestral Thames probably ran originally at around the same elevation as the current Thames in the region (~ 33 m OD). The Gap has always been the route of the Thames and, although it does initially look difficult to see how the current (wimpy, misfit) version of the Thames could drill through the Chilterns, in fact it's more that the Chilterns rose across its course and forced it to cut down. Compare the Indus and Bramhaputra for a much more spectacular case when the Himalaya rose across their courses. Palaeogeo (talk) 13:22, 29 January 2023 (UTC)

Images

The images need to be re-created, but without the title and footer text. See MOS:TEXTASIMAGES — GhostInTheMachine ^{talk to me} 21:45, 13 February 2024 (UTC)