This follows on the previous post here of an ongoing series of maps created for outlets that aren't necessarily on the web - see label:revisit here and label:3D here - this is partly because I'm disengaging from socials; and that itself was partly because I had to let go of significant chunk of work on the internet for lack of resources (see §2 here). See my remaining web presence in the banner menu of the web view here.
Valriepieris Circle
As part of my engagement via XR* Tell the Truth & Quakers Support for Climate Action, I looked at the extent of the Valriepieris Circle encompassing half the world's population in SE Asia. Using various datasets and tricks explained in the ms. here, I created this globe view with basic geomorphology:
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| click to enlarge, full size here & TIFF here |
Bay of Biscay
Outside socials I stay on mailing lists, and my friend John Nelson posted this "trippy map" here in his "please steal this" series also on YouTube here. I made a mistake in grabbing GEBCO sea floor map 2025 update here... as a 3D file & not as a geoTIFF!
I'm currently in SW France, and the near-shore Bay of Biscay near Biarritz has not one but two underwater canyons: not unlike offshore Monterey Bay, I loved to visit when in So. Cal. some 20 yrs ago; both have so-called flysch bedrock explained in the notes below, also here.
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| click to enlarge, full size here |
Latest GEBCO topo-bathy data was loaded for the Bay of Biscay area offshore SW France and NW Spanish Cantabria. The Esri Scene above looks almost East toward Southwestern France. The narrow Adour River mouth canyon (top right, river in blue) jumped from the wider pre-Glaciation mouth canyon farther left or North. Note the river on the Cantabrian coast (mid left) has no such mouth.
The rough Spanish coast reflects the fact that the geology grain of upturned strata (see Costa Quebrada Global Geopark here and some set locations of Game of Thrones here) run parallel to the coast (see mountain range at far right) and erosion follows weak strata. In the Adour River mouth strata are also upturned (as in Bay of Biarritz) but the coast is perpendicular: the cuts go straight along the geologic grain.
The jump toward the mountains is counter-intuitive: as mountains build up to the right or South, and erosion accumulates in the top center, one expects rivers to move left or North: therefore, the mouth and canyon should shift North not South. What happened is that the Garonne River mouth, currently at the Gironde Estuary visible top center, used to have its mouth at the older canyon of the pair, to the North or at left.
The Cantabrian mountains are seen at far right, & the Pyrénées are off the map above at right, East & South. As erosion & mountain building elevated the South at right, the Adour River to the South captured part of the flow of the Garonne River**. The Garonne continued Northwest on its current course. The Adour to the South ran parallel to the Pyrenean foothills off the map upper right. Its significant sediment load created the deeper narrower canyon offshore its current mouth**.
The slight offset between the mouth of the river in blue & its canyon remains unexplained. As Bayonne has canalized the Adour, is it another case like the Morganza Spillway keeping the Mississippi from jumping its banks and protecting New Orleans (Wikipedia)? The closest US analog is the Monterey Canyon here: both geologic provinces have flysch deposits; the Cantabrian coast is also called the Flysch coast here or cliffs here.
*Extinction Rebellion maps: risk of flooding from river & from sea for East Anglia & Herefordshire here, London here, and Thames Barrier here.
**More counter-intuitive geomorphology (the study of landforms):
1: principles
- rivers cut valleys from their mouth at the coastline backward up the coastal plains and the piedmont to the source at the mountains
- rivers like glaciers carved not thru water or ice flow, but by abrasion via silt, sand, gravel even boulders they carry, called sedimentary load
- before & after carving the mouth canyons & montane areas, heavy sedimentary loads can be dumped in the piedmont &/or plains: when flow energy drops, so does the capacity to carry sediment and they’re left in levees; these can ironically put rivers above their surrounds, as illustrated in East Anglia at lower left here (blog here: Topography & Geomorphology).
2: narrative (geological reasoning from North American & West Asian analogues, neither fieldwork nor literature review)
- as the roughly East-West Pyrénées rose, the Adour running parallel and in front of them carved back or East into the erosional apron immediately North of the piedmont
- the Garonne River flowing Northwest from further East emptied into the current Bay of Biscay, and had its mouth at the old canyon further North and left than the current mouth of the Adour River
- as the piedmont rose as did the erosional apron, the Garonne was pushed further North to the current Gironde Estuary, stranding the North older canyon
- the Adour River carving back toward the upstream section of the Garonne, eventually captured part of the Garonne flow to go East along the piedmont
- its increased water flow, combined with increased sedimentary load from the rising piedmont & erosional apron, resulted in sharper & deeper Southern canyon to the right
