Integrative Natural History of Minnesota's North Shore, Part 4: Of Desire Lines and Hydrant Flags | Duluth
My final photo showing geological aspects of the great baymouth bar known as Minnesota Point. We're still on the grounds of the Park Point recreational facility. And we're facing northward, toward Lake Superior.
In the snowier parts of the US, fire hydrants are now equipped with little red flags mounted on tall, flexible staffs. They may partly be there to help firemen locate the hydrants after a blizzard. But, as I understand it, they're primarily intended to keep snow plows from running over buried hydrants and inadvertently causing wintertime geysers and ice cascades.
Having seen snow-plow drivers on my own home turf wreak a lot of damage on human infrastructure, I can believe it. Here, however, the flag appears to be missing and the white-and-Dayglo-yellow staff seems to serve another purpose.
Behind this hydrant stands the crest of one of the crescentic dunes mentioned in this series' Part 2 and Part 3. The bare patch in its middle is what park planners call a desire line. That's an informal path created not by designers but by visitors who, like whitetail deer, forge their own preferred shortcuts through existing vegetation. (Note the nice assortment of footprints in the sand above the hydrant.)
On either side of the desire line, the trees and shrubs are still doing a good job of keeping windborne sand particles from migrating shoreward (toward the camera). You can easily see how the plants' stems and foliage act as baffles and slow the air speed to the point the grains drop to the surface again.
But that bare patch created by the trampling of countless feet marching their way toward the beach has given the wind just the opportunity its needs. Unencumbered by any barrier, the sand has come spilling over the crest like a wave of invading Marines. And the invasion has been successful: now there's a broad, tonguelike fan of sand on the lee side of the dune ridge.
These tongues of pure, bright-tinted sand can be spotted both on Google Earth aerial view and USGS National Map lidar imagery. In this spot, the migrating sand threatens to completely bury the main portion of the hydrant, which I suspect has to be dug out periodically.
In the two preceding parts of this series (see the links above) I speculated on what the prevailing wind direction on Minnesota Point must be, and on whether the crescentic dunes that cover it are parabolic or barchan. Given all this abundant sand transport away from the lake, from northeast to the southwest, it appears that northeasterly onshore breezes play a more important role in this locale than the regional westerly winds.
And that rather supports my barchan hypothesis. Still, nature is both subtle and complex, and other unheeded factors may also be involved.
To see the other photos and descriptions of this series, visit
my Integrative Natural History of Minnesota's North Shore album.
Integrative Natural History of Minnesota's North Shore, Part 4: Of Desire Lines and Hydrant Flags | Duluth
My final photo showing geological aspects of the great baymouth bar known as Minnesota Point. We're still on the grounds of the Park Point recreational facility. And we're facing northward, toward Lake Superior.
In the snowier parts of the US, fire hydrants are now equipped with little red flags mounted on tall, flexible staffs. They may partly be there to help firemen locate the hydrants after a blizzard. But, as I understand it, they're primarily intended to keep snow plows from running over buried hydrants and inadvertently causing wintertime geysers and ice cascades.
Having seen snow-plow drivers on my own home turf wreak a lot of damage on human infrastructure, I can believe it. Here, however, the flag appears to be missing and the white-and-Dayglo-yellow staff seems to serve another purpose.
Behind this hydrant stands the crest of one of the crescentic dunes mentioned in this series' Part 2 and Part 3. The bare patch in its middle is what park planners call a desire line. That's an informal path created not by designers but by visitors who, like whitetail deer, forge their own preferred shortcuts through existing vegetation. (Note the nice assortment of footprints in the sand above the hydrant.)
On either side of the desire line, the trees and shrubs are still doing a good job of keeping windborne sand particles from migrating shoreward (toward the camera). You can easily see how the plants' stems and foliage act as baffles and slow the air speed to the point the grains drop to the surface again.
But that bare patch created by the trampling of countless feet marching their way toward the beach has given the wind just the opportunity its needs. Unencumbered by any barrier, the sand has come spilling over the crest like a wave of invading Marines. And the invasion has been successful: now there's a broad, tonguelike fan of sand on the lee side of the dune ridge.
These tongues of pure, bright-tinted sand can be spotted both on Google Earth aerial view and USGS National Map lidar imagery. In this spot, the migrating sand threatens to completely bury the main portion of the hydrant, which I suspect has to be dug out periodically.
In the two preceding parts of this series (see the links above) I speculated on what the prevailing wind direction on Minnesota Point must be, and on whether the crescentic dunes that cover it are parabolic or barchan. Given all this abundant sand transport away from the lake, from northeast to the southwest, it appears that northeasterly onshore breezes play a more important role in this locale than the regional westerly winds.
And that rather supports my barchan hypothesis. Still, nature is both subtle and complex, and other unheeded factors may also be involved.
To see the other photos and descriptions of this series, visit
my Integrative Natural History of Minnesota's North Shore album.