Here is a new map (based on a computer-generated terrain map from Henry Patton) showing the "landscape context" for Rhosyfelin. The "lighting" for this model is in the south, so the north-facing slopes show up clearly. Click to enlarge.
Rhosyfelin is shown with the orange dot. The "basin" which is supposed to have held the waters of Glacial Lake Brynberian is clearly shown, defined in part by the northern slopes of Mynydd Preseli.
Brian,
ReplyDeleteRhosyfelin seems to be near the bottom of the basin of Glacial Lake Brynberian. It would be the last place to drain dry when the glacial lake drained of its meltwater.
Do we know when the Lake formed? And how long it would have taken to drain?
Kostas
It's certainly worth thinking about that the gorge of the Afon Brynberian might have been fashioned -- at least in part -- by the draining of Lake Brynberian. The trouble is that it runs in the wrong direction -- glacial spillways tend to run AWAY from the ice edge or ALONG the ice edge. It would be very rare indeed for glacial drainage to occur beneath the ice dam -- that would defy the laws of physics. It happens sometimes in Iceland with jokulhlaups -- but there are strange things going on there, associated with volcanoes...
ReplyDeleteBrian,
ReplyDeleteThanks for your commend. Interesting.
In a previous post I talked about the possibility of meltwater running on the surface of an ice sheet in a direction opposite to the glacial advance or drain channel. If we were to assume (for just this once) Glacial Lake Brynberian was at one time solidly frozen and latter melted from the 'top-down', would this scenario agree with the evidence on the ground?
Kostas
No
ReplyDelete