The parking lot puddle revisited
Yesterday, I showed you these photos...
...and asked you to guess what they reminded me of.
Man, there were some great ideas people pitched forward! I was really impressed. One person even came up with the same idea that occurred to me!
Okay, so clearly what we've got here is a puddle that's drying up right? Some leaves and other botanical debris fell into the puddle and has thus become concentrated in this spot.
The pattern I noticed was a linear pile of debris [consisting mainly of the woody little "petals" of the tulip tree (Liriodendron tulipifera) "flower"] as well as a dark color due to being damp. The edge of the damp patch parallels the edge of the linear tulip tree debris field. I think the way this formed was that in the puddle's earlier (larger) state, it was deep enough for the tulip tree "petals" to float, and wind pushed them all over to the same side of the puddle (the southern edge). As the puddle dried out, this stranded flotsam preserves either an earlier "shoreline" or an offshore parallel to the shoreline. (The second possibility would apply if the "petals" were too big to get pushed all the way to the actual shoreline: they may run aground some distance "offshore.")
This brought to mind the relationship between a continental ice sheet and the end moraine it leaves* behind. Glaciers expanded outward, reach their maximum size, stay there for some amount of time, flowing along and depositing a scum of debris all along their edges. Later, they melt back, or possibly melt away entirely. However, the debris belt marks how far out they once reached. Here's a geological equivalent, in a map** showing end moraines (green) in Minnesota, Iowa, and South Dakota:
As the moraine marks the former extent of the glacier, so too does the stranded line of tulip tree flotsam mark the former extent of the puddle. Fresh from my lectures on glaciation and the Ice Ages, I got the sense I was looking from west to east across North America, seeing Canada recently scraped clean (wet areas) and the far-right ("south") accumulation of tulip tree petals morphed in my mind into a terminal moraine complex.
The main problem with this analogy: puddles are standing water, not flowing ice. Still, I can't help but see a similarity in process, regardless of the huge differences in scale and materials. I see the world through geology-colored glasses.
_______________________________________
* no pun intended
** From the U.S.G.S.'s "Glacial map of the U.S. east of the Rockies, west half" (1959)," via here
...and asked you to guess what they reminded me of.
Man, there were some great ideas people pitched forward! I was really impressed. One person even came up with the same idea that occurred to me!
Okay, so clearly what we've got here is a puddle that's drying up right? Some leaves and other botanical debris fell into the puddle and has thus become concentrated in this spot.
The pattern I noticed was a linear pile of debris [consisting mainly of the woody little "petals" of the tulip tree (Liriodendron tulipifera) "flower"] as well as a dark color due to being damp. The edge of the damp patch parallels the edge of the linear tulip tree debris field. I think the way this formed was that in the puddle's earlier (larger) state, it was deep enough for the tulip tree "petals" to float, and wind pushed them all over to the same side of the puddle (the southern edge). As the puddle dried out, this stranded flotsam preserves either an earlier "shoreline" or an offshore parallel to the shoreline. (The second possibility would apply if the "petals" were too big to get pushed all the way to the actual shoreline: they may run aground some distance "offshore.")
This brought to mind the relationship between a continental ice sheet and the end moraine it leaves* behind. Glaciers expanded outward, reach their maximum size, stay there for some amount of time, flowing along and depositing a scum of debris all along their edges. Later, they melt back, or possibly melt away entirely. However, the debris belt marks how far out they once reached. Here's a geological equivalent, in a map** showing end moraines (green) in Minnesota, Iowa, and South Dakota:
As the moraine marks the former extent of the glacier, so too does the stranded line of tulip tree flotsam mark the former extent of the puddle. Fresh from my lectures on glaciation and the Ice Ages, I got the sense I was looking from west to east across North America, seeing Canada recently scraped clean (wet areas) and the far-right ("south") accumulation of tulip tree petals morphed in my mind into a terminal moraine complex.
The main problem with this analogy: puddles are standing water, not flowing ice. Still, I can't help but see a similarity in process, regardless of the huge differences in scale and materials. I see the world through geology-colored glasses.
_______________________________________
* no pun intended
** From the U.S.G.S.'s "Glacial map of the U.S. east of the Rockies, west half" (1959)," via here
Labels: analogies, contest, glacial landforms, glaciation, iowa, minnesota, nova, plants, south dakota
4 Comments:
very cool observation! Makes me think about repeating forms and shapes in nature, and the idea that nature may be fractal.
Funny, evaporation didn't even occur to me. ?!
Perhaps due to the field of view in the shot, I figured the water level dropped because it slowly flowed along the curb elsewhere.
Evaporation though makes perfect sense too.
tom donlon
"depositing a scum of debris"
Hey! I grew up on a scum of debris, thats not a very nice thing to say about Long Island. (Although very apt in many cases)
You see these lines of seed deposits on river bars, and if conditions are right, they turn into lines of small trees. In a multi-year drought, they might attain some size and density, and be a major force in determining channel pattern. The lines of small sycamores you see on bars started like this.
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