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, aussi en français ici.
click to enlarge, full size here
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 in the upper left hand inset in the scene above is a cartographic error: the onshore roads & rivers dataset don't match the mouth of the river with the newer right hand Southern canyon in the offshore bathymetry; this often happens with divergent data sets with differing metadata &/or simple data errors. See below the 1:1M geologic map of France from IGN (here) posted on the same map as the offshore bathymetry. That is not in fact a B&W image, but a so-called overlay to allow the overlap of different datasets and avoid obscuring each other. Note the fabulous detail that brought up for the bathymetry.
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| click to enlarge, full size here |
In the geologic map, in red-dotted yellow is the erosional apron, that is the wedge of rocks spreading north from the erosion of the Pyrenees to the south. The Adour River has the arcuate track seen at centre left: its mouth lines up correctly with the new canyon to its left or West. The Garonne River angles Northwestward across the middle toward the Gironde Estuary at center top to the North: it starts flowing NNW near the mountains, then angles NW in the mid section, and pops back NNW before the estuary; if you line up the midsection and extend it to the Bay of Biscay, you see that imaginary line go over Arcachon Basin notch along the coast at centre left, and meet the ancient canyon at centre left to the West.
Voilà! The power of GIS marrying datasets to draw visually arresting conclusions.
*Extinction Rebellion maps: risk of flooding from river & from sea for East Anglia & Herefordshire here, London here, and Thames Barrier here.
**Short explanation of 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
