A classic example of these linear landforms (perhaps even the best examples of these). As some food for thought, and perhaps somewhat counter-intuitively, the largest of these features are slightly positive forms (i.e. raised).
If you are new to WoGE: give approximate coordinates of the image and a brief description of the features and their origin.
1) The Schott Rule is in effect (i.e. one hour answer posting moratorium for every previous win).
2) To make things a bit more interesting, I have purposely removed the scale bar though there are plenty of clues (cadastre, etc) that should make this obstacle a mere speed-bump. Speaking of cadastre, it should also help narrow down the geographic area a bit.
Enjoy!
Jerome
Wednesday, May 19, 2010
WoGE #205
A classic example of these linear landforms (perhaps even the best examples of these). As some food for thought, and perhaps somewhat counter-intuitively, the largest of these features are slightly positive forms (i.e. raised).
If you are new to WoGE: give approximate coordinates of the image and a brief description of the features and their origin.
1) The Schott Rule is in effect (i.e. one hour answer posting moratorium for every previous win).
2) To make things a bit more interesting, I have purposely removed the scale bar though there are plenty of clues (cadastre, etc) that should make this obstacle a mere speed-bump. Speaking of cadastre, it should also help narrow down the geographic area a bit.
Enjoy!
Jerome
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I've made a couple of small edits to the original post. They are in italics.
ReplyDeleteJerome
Um, dust devil tracks in the exurbs of a Martian city?
ReplyDelete49 32'53.74"N 97 01'00.05"
ReplyDeleteIn Ontario Canada, north of Winnipeg.
The features are iceberg keel marks in Glacial Lake Ojibway. I guess if there are raised features they must be glacial push ridges but I can't tell which are which (I'd love to hear more).
Simon,
ReplyDeleteWell done on the location (except we are south of Winnipeg!) and your guess for the features is spot on. These are indeed iceberg keel marks formed in Glacial Lake Agassiz (Ojibway is close enough as Agassiz and Ojibway were connected at some point in time). In any case, they were produced as icebergs calved into Lake Agassiz from the ice front to the north. katabatic winds of the ice sheet surface likel pushed these toward shore. Some keel mark likely result from the ice berg grounding in the shallow parts of the basin. Other keel marks (usually shorter and with more of a crater at one end) result from iceberg overturning and dragging on the lake floor during the rotation.
Now, regarding the raised elements. You are right that some features result in part from a pushing process as the keel efectively ploughs a furrow and produces a set of berms on either side. However, there is an additional element to their appearance.
After their formation, furrows were filled by silt from density underflows entering the lake basin and clay from suspension settling during winter. After drainage of Lake Agassiz, it has been suggested that sediments dewatered and compacted, with the greatest effect of this affecting the clays, while silt largely maintained its original volume. In this way, silt-filled iceberg scours became ridges.
Nice job on the guesses. WoGE #206 is all yours.
Simon,
ReplyDeletePlease post a notice here once WoGE#206 is available.
Jerome
Jerome,
ReplyDeleteVery interesting geology indeed...
I've picked a bit of Google Earth, but I don't have a blog to post on. Would you mind hosting it on here?
I guess I could create a one-off blog like you have, but it would take me ages to think up as good a name as you did ;->
If you're willing, I guess I send through the image and some text. Via email?
Let me know what you prefer.
Simon
Simon,
ReplyDeleteNo problem for me to post your image. send it by email at: jeromelesemann@hotmail.com
I'll post it as soon as I receive it.
Jerome
WoGE #206 is now posted at:
ReplyDeletehttp://sedimentsexactly.blogspot.com/2010_06_01_archive.html