Friday, April 12, 2019

News of My Old Tree Friend & Two New Ones

A lovely spring day in Laramie, Wyoming. 

Though spring has officially arrived, I knew I wouldn’t find any visible changes in the two trees I’m following. Here in the continental interior at 7200 feet elevation, it’s too early for flowers or leaves on trees. But there is one exception—the American pussy willow, Salix discolor. So before I checked on the trees by the art building, I walked up “Willow Canyon” just east of town to see how the willow was doing.

I discovered this willow on a hike in late February, 2015. Catkins were already emerging! Just the tips were visible, but still I was astonished, and chose the willow as the tree to follow that year. And of course it soon became “my willow” … trees are that way.
A full healthy canopy; August 2015.
I still visit my willow periodically. It's a beautiful tree when fully leafed out, but last August I discovered to my horror that all the leaves were dead! It was much too early for annual leaf fall, so I presume it was because of our drought. “What does this mean?!” I was worried

 … and I was really happy yesterday when I found it covered in catkins :-)
Willow standing behind two junipers.
Tiny white dots are catkins, not snow.
A few dead leaves still hang on ... imagine the canopy full of these!
Occasionally the sun broke through the clouds, making the catkins shine.
These catkins are not as far along as those of April 2015 (below). I'm not surprised. We're having a cool snowy spring. But snowy is fine—we need the moisture.
April 2015.
By the time we got back to the car, the snow had stopped and the sun was out, lifting my spirits even more. Off to the art building!

The late afternoon sun partially lit the two trees I'm following this year, highlighting their beautiful bark. As I suspected, I found no clues as to identity. The buds didn't help (do you recognize them?)
Next I visited the castle ... still no signs of residents. Maybe they're snug and warm inside, and haven't bothered to shovel the walkway.
The woman standing by the entrance last month was still there. And not even shivering!
Nor was I, but my hands were cold after taking photos (no gloves), so I went inside to enjoy the artwork. Student exhibitions change monthly, which is nice for a tree follower. I took photos of a piece I found especially appealing—something about the color and form.
Lattice by Donatellia Austin, 2018; Paper, Fabricated Steel.

I wondered if anyone would tell me not to photograph the artwork, but the few people who walked by said nothing, didn't even glance my way. Then I looked up and realized ... I was being watched!


For more tree-following news, see April's virtual gathering kindly hosted by The Squirrelbasket. And again, thanks to Lucy Corrander who started the whole wonderful business years ago.


Monday, April 1, 2019

Big Hollow—an Exceptional Hole in the Ground

Aeolus—Greek god of the wind and sculptor of the Big Hollow.

In the Laramie Basin just west of Laramie lies an exceptional hole in the ground—the Big Hollow. It is indeed big: nine miles long, four miles wide, almost 200 feet deep in places. In 1980 it was designated a National Natural Landmark, not just for its size but also for its origins. The Big Hollow was dug by wind!

Laramie residents know the power of wind. It drives turbines, knocks over semi-trucks, builds huge snowdrifts that close highways, and sends hoards of tumbleweeds racing into town. Spring breezes reach 35 mph, with gusts to 65 or more. Yet the wind was even worse during the last Ice Age. That’s when it excavated the Big Hollow, the largest deflation hollow in North America and a classic example of topographic reversal.
The Big Hollow is a product of deflation—excavation by wind.  Even more astonishing, it was once a hill and its rim was a drainage bottom! Details to follow.
The green and white roughly-circular features within the blue oval are small deflation hollows occupied by internally-drained saline lakes and playas (modified Google Earth photo).
Huge as it is, the Big Hollow is easy to miss. While a mountain range stands above its surroundings, where it can be readily admired, a hollow lies below and is easily overlooked. But it doesn’t have to be that way. West of Laramie, US Highway 130 traverses the north rim. Look south from the road to grasp the immensity of the Big Hollow (even at 70 mph).
View across Big Hollow from the north rim; arrow points to the south rim.

How did wind blow away so much land? And why here specifically? To understand, let's visit the rim of Big Hollow 200,000 years ago. Bring an extra-warm coat and a snug-fitting hat!
Medicine Bow Mountains and adjacent Laramie Basin during the last Ice Age; by Samuel H. “Doc” Knight, Mr. Geology of Wyoming and master of block diagrams (modified from Knight 1990).
It’s the height of the Ice Age, and even though we’re 500 miles south of the continental ice sheet, the impact is obvious. The Medicine Bow Mountains to the west are buried under a thick layer of ice and snow, with only the high Snowy Range visible. Glaciers extend down drainages, and frigid meltwater streams rush out into the basin. There they slow and drop their loads of eroded debris, spreading gravel and rocks across the land.

The Laramie Basin is a scene straight out of the arctic. It’s covered in permafrost, a thick layer of soil frozen year round. The immediate surface thaws during warmer months, but the season is too short and dry for much to grow. Into this harsh barren world, a cold west wind roars down from the Medicine Bow Mountains.

The biggest surprise is the immediate landscape—it’s turned on its head! We’re standing not on a rim but in a drainage bottom, on a floodplain covered in rocks and gravel carried down from the mountains. And look south. Instead of a giant hollow, there’s a hill!
Big Hollow in early to mid Pleistocene time.

As we travel the 200,000 years back to the present, we will carefully watch the wind dig the Hollow so that we can understand how the landscape was changed so dramatically.

Several things are needed for a deflation hollow in addition to wind. There must be material light enough to be blown away. The Laramie Basin meets this requirement. The bedrock is soft shale that can be churned up by freeze-thaw, and crumbled into dust and dirt. With so little vegetation, the loose material readily blows away.

But a hole is more than empty space. It needs a rim and sides to define it. In the case of the Big Hollow, the rim consists of a layer of rocks and gravel left by a former tributary of the Laramie River. They’re too heavy for wind to carry off, and form a wind-resistant cap that protects the underlying shale from erosion.
Gravel and rocks on the rim are often cemented with caliche—a naturally-occurring cement (calcium carbonate).
As we time-travel back to the present, we watch the wind erode and lower the shale surface bit by bit, year after year, while the erosion-resistant gravel-capped surface stays relatively high. Geologists call this topographic reversal. A high point on the landscape becomes low, and the old lowland is left standing high. The Big Hollow is a National Natural Landmark in part because it’s a classic example of topographic reversal.

Here's topographic reversal in action (modified from Mears 1987):

First, a former tributary of the Laramie River spreads gravel and rocks from the Medicine Bow Mountains across the floodplain, next to a hill made of shale. 

Next the stream shifts course, abandoning the channel. Wind erodes the shale faster than the gravel and rocks.

Today the old drainage bottom is a high point (rim), and the hill has become the Big Hollow. “The hollow represents a classic case of ‘topographic reversal …’” (National Park Service).

Tour the Big Hollow

This tour starts in Laramie and makes a clockwise loop around the Big Hollow via US Highway 230, the Big Hollow Road (well-maintained gravel), and US Highway 130. It can be done in winter but check road conditions first. Most of the land is privately-owned, limiting us to views from roads; exceptions include several public lakes (turnoffs signed).

From the junction of US Highways 130 and 230 in Laramie, take 230 west eight miles and turn right on Pahlow Lane. After about five miles, turn right on Big Hollow Road, County Road 44. Shortly pass Twin Buttes Reservoir on the left; now pay close attention. After about 1.5 miles, the road starts to climb the south rim of the Hollow. It's not as prominent as the north rim and easy to overlook. Leave the south rim at the warning sign (40 mph) and drop into the Hollow. Note the north rim beyond (geo-geek photo op!).
Cross the narrow west end of the Hollow, passing the Big Hollow anticline (fold) on the right, marked by a small oil field. The road then winds up to the north rim. Near the top, stop to study small road cuts exposing the rocks and gravel that cap the rim.
At the junction with US Highway 130, pull off on the right side of the Big Hollow Road. Take advantage of this opportunity as pullouts are scarce along 130. Saunter back down the gravel road to admire the Big Hollow.
Turn right (east) onto 130, toward Laramie. Read your odometer or set it to zero. For the first mile, the highway runs close to the rim with good views of the Hollow, but unfortunately there are no pullouts. At 3.5 miles, you might want to stop at the Overland Trail historical marker—a sizable pullout but on the wrong side of the road.

About six miles from the Big Hollow Road, pay close attention. At 6.3 miles, take an unmarked turnoff right (this is across the highway from green mile marker 7). Note the unlocked gate and sign. This is State land, accessible to the public. Go through (and close) the gate, and park on the rim. Be careful getting off and on US 130. It can be busy, especially on weekends, and the speed limit is 70 mph.
The gate is easy to operate.
Here on the rim, the ground is littered with gravel and rocks from the Medicine Bow Mountains, carried down by that former tributary of the Laramie River. After strolling along the ancient stream, you can walk south down into the Hollow not quite a mile before reaching private land.
Back on the highway, continue east (right) toward Laramie, passing the east end of Big Hollow just before the airport. A few more miles takes you into town and back to the junction with US 230.
View west across Big Hollow. The old stream channels that form today's rims joined near the airport (large X). Red arrows approximate tour route. Modified from Mears 1987.

Sources

Blackwelder, E. 1909. Cenozoic history of the Laramie region, Wyoming. J. Geol. 17(5): 429-444.

Hausel, W.D., and Jones, R.W. 1984. Self-guided tour to the geology of a portion of southeastern Wyoming. Wyoming State Geological Survey Public Information Circular 21, 44 p., 1 pl., scale 1:500,000.

Knight, SH. 1990. Illustrated geologic history of the Medicine Bow Mountains and adjacent areas, Wyoming. WSGS Memoir No. 4.

Mears, B, Jr. 1987. Late Pleistocene periglacial wedge sites in Wyoming: an illustrated compendium. Geological Survey of Wyoming Memoir No. 3. [see Introduction for information about Big Hollow.]

Mears, B, Jr. 1991. Laramie Basin, p. 418-427 in Rehis, M.C., Palmquist, R.C., Agard, S.S., Jaworoski, C., Mears, B., Jr., Madole, R.F., Nelson, A.Rr, and Osborn, G.D.1991. Quaternary history of some southern and central Rocky Mountain basins, Ch. 14 in Morrison, R.E., ed. Quaternary nonglacial geology: conterminous U.S., in GSA, The Geology of North America Volume K-2.

Steele, K., Fisher, S.P, and Steele, D.D. n.d. (after Jan 2012). The Big Hollow in Geology of Wyoming. https://www.geowyo.com/big-hollow.html (accessed February 25, 2019).


Wednesday, March 13, 2019

Tree-Following—the Chosen One

Actually two.

I’ve chosen a tree to follow, actually two—a pair growing next to the building that houses the Department of Visual & Literary Arts at the University of Wyoming. They were planted on the order of seven years ago according to an art professor (medium oil) whom I met during my recent visit.

What kind of trees are they? I don’t know. It will be fun to figure this out as leaves, flowers and fruit appear.
They're small trees, with sturdy trunks and limbs, intricately branched canopies, and attractive mottled bark. I suppose they're an ornamental cultivar.
In keeping with the style of older buildings on campus, the wall behind the trees is covered with sandstone. These aren’t full blocks. They might be split-face stones fabricated from quarried pieces  except that there’s a suspicious uniformity about them.
Another mystery.
The art building offers opportunities for photography in the abstract, which I enjoy. It encourages creativity and concentration … compose, shoot, compose, shoot … pretty soon the rest of the world disappears.
Probably the inhabitants of this building won’t think it odd that I visit these trees monthly, photographing them and their surroundings from various heights and angles. Maybe they will think I’m just another art student.
 
In a shady corner behind the trees, I found a castle! Do fairies live here? This time of year it’s hard to say. Probably they go south for the winter. Or do Wyoming fairies hibernate? Maybe they’re cold-tolerant … so much to learn!

We tree-followers visit our chosen subject once a month, and share news, photos and thoughts at virtual gatherings kindly hosted by The Squirrelbasket. More information here, including how to join in the fun.

Saturday, March 2, 2019

Where does the dust come from?

all we are is dust in the wind… By Laszlo Bartha, CC BY 2.0.

Sometimes we find wisdom in dust. As metaphor, it hints at how we might best live. Dust in the wind, all we are is dust in the wind. Dust returns to the earth as it was. Ahhh  make the most of what we yet may spend, before we too into the dust descend; dust into dust, and under dust, to lie sans wine, sans song, sans singer, and  sans End! (1)

But this time of year it can be hard to appreciate the philosophical side of dust. The wind blows and blows and blows, the snow melts exposing bare soil, and dust takes to the air—landing on windshields, in eyes, up the nose, and throughout the house. So I felt fortunate to stumble upon a short tale that turns this annoyance into something a bit magical.

From Where does the dust come from? by Ermilo Abreu Gómez (2):
The dust that sticks on the windows, on the statues, on the books and on the canvas of paintings, doesn’t come from the earth. It comes from the wind. It is the wind itself, dying of exhaustion and thirst in the nooks and crannies of our possessions. 
Lifeless remains of the wind (house dust up close, from PRI).

Notes

(1) From Kerry Livgren and Kansas, Dust in the Wind; the Hebrew Bible, Ecclesiastes 12; and Edward FitzGerald, The Rubáiyát of Omar Khayyám (XXIII).

(2) My translation from Spanish, here's the original (suggestions welcome):
El polvo que se pega en las ventanas, en las imágenes, en los libros y en la tela de los retratos, no viene de la tierra. Viene del viento. Es el viento mismo que muere de cansancio y de sed en el rincón de las cosas íntimas. ¿De dónde viene el polvo? – Ermilo Abreu Gómez
Read the full story here (it’s short).