When will the leaning tower of pier fall?

Bridges don’t last forever. Some fall, some are taken down. And some crumble away one piece at a time.

Anyone who has walked across the Stone Arch Bridge in Minneapolis has probably noticed a lonely stone pier — now just a masonry flower pot and avian rest spot — in the middle of the Mississippi River.

The pier was once part of an 1874 iron bridge that was built to connect the two young cities of St. Anthony and Minneapolis, and to transport lumber by wagon from east bank sawmills to trains heading west. The pier is losing stone blocks at a brisk pace. Here’s how it looked last winter:

It’s also listing. If you take the railing of the Stone Arch to be vertical, the pier is definitely half a bubble off.

Before the pier disappears altogether, I thought I should run a few images of the Lower Bridge, also called the Tenth Avenue Bridge, in its heyday.

The King Iron Bridge and Manufacturing Company built it.

Minnesota Historical Society photo

And here it is, attracting a crowd and a few wagons. You can see the stone piers in the river and the iron truss beneath the deck. The Stone Arch Bridge is nowhere in sight because it hasn’t been built yet. I think that’s a train in the background.

Minnesota Historical Society photo

A later photo includes the far sturdier Stone Arch Bridge. On the east bank, both bridges ended at Sixth Avenue SE. On the west bank, the Lower Bridge ended at Tenth Avenue South, which is now Gold Medal Park.

Minnesota Historical Society photo

Horses pulling carriages still clip-clop across the river. The carriages are more likely to carry tourists and newlyweds than lumber, but now they have to cross on the Stone Arch because the Lower Bridge was dismantled in 1943.

Minnesota Historical Society photo

It wasn’t sturdy enough for modern, smoke-belching forms of transport. The iron truss was probably recycled to help build World War II tanks or other war materiel.

Why did the bridge removers leave one pier in the river? I asked a National Park Service ranger that question a few years ago and got a shrug. The answer might be lost in the Mississippi mud.

But the crumbling pier begs another question: when will it fall down? Hard to say, as they say. Entropy always wins in the end, but the disintegration could stall. I’m going to take a wild guess and say next spring after the winter ice beats it up.

Send in your guess.

Thanks to the Minnesota Historical Society for permission to use several historic photos from its collection.




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Somebody laid eggs on my bur oak branch

I’m tracking the passage of the seasons by following a branch on a stately old bur oak at the University of Minnesota.

The season hasn’t changed, of course. It’s still summer, and, in fact, the temperature in my neighborhood probably jumped last week with all the students wandering around looking for classes and waiting for buses.

But the start of school feels like fall, a correlation that’s hard-wired into most of us, so I went over to the tree last week to take a look.

The campus may have been sleepy this summer, but my branch looked as though it had seen plenty of activity. Here’s how it looked a few months ago on the solstice:

The picture of arboreal innocence and optimism — velvety leaves, fuzzy new branch growth. But last week there were holes in the leaves and a mysterious black knob.

For help with interpreting what I saw, I sent my photos to Jana Albers with the Minnesota Department of Natural Resources. She said that my photos showed evidence of eating and egg-laying.

First the eating.

Picky eaters just go for the green part

Beetles, the kind that prefer green cells, not the tough leaf-vein cells, probably nibbled on this leaf, she said, and left behind the lacy holes.

Somebody else, a less discriminating eater, chewed a jagged hole in another leaf.

Wholesale munching here

It was probably a forest tent caterpillar. No delicate nibbling with forest tent caterpillars. They gobble everything — tender green cells and the tougher vein cells. Forest tent caterpillars are native to Minnesota, and this oak tree certainly isn’t being eaten to death by them. Still, it was a little disconcerting to discover evidence of them.

On to the egg laying.

A moth apparently took advantage of my oak branch to start the procreation process.

See if you can count the eggs!

The dark round object surrounding the branch is an egg mass, probably deposited (laid?) by some kind of moth. Albers said she couldn’t tell which kind of moth, but she suggested I look for fifty to one hundred tiny caterpillars emerging next spring.

This was starting to feel like Charlotte’s Web.

My branch has no acorns on it, but other branches on the tree undoubtedly do because the tree is starting to drop them. Bur oaks drop their seeds between August and November. Some of the oaks nearby had dropped a lot, but there were only a few beneath my tree. On this day, they cast long shadows across the sidewalk in the late afternoon sun.

Bur oak acorns hide inside a bristly fringed cap

The university is no longer sleepy. Standing near my tree in front of Eddy Hall, I saw quite a few of those students doing the fall thing — wandering around, waiting for buses. I also watched a young man (black car, lower left in the photo below) spend nearly an hour at the intersection. The engine was idling, but he was busy. Texting. Hope he didn’t miss any classes.






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Hordes of bicyclists on my secret bridge?

Welcome back, University of Minnesota students! In honor of the annual boost in the neighborhood’s bicycling population, I’m offering a photo tour of the proposed U of M Bikeway route.

First, a map. The city of Minneapolis website shows the trail, which will start on the east bank of the Mississippi River, run through the Dinkytown Trench — a low spot in the landscape that used to be a creek bed — and end a mile or so later at Fifth Street SE near TCF Stadium.

Proposed U of M Bikeway

Today two dirt roads parallel a set of mostly-abandoned railroad tracks in the trench. The city had hoped to use the straighter, wider path (on the left in the photo below), for the new bikeway.

The view is from the little suspension bridge near Sanford Hall on University Avenue

But the railroad owned the property, and dealing with railroads is muy complicado. A “long list of disagreements” finally convinced the city to shift the route to the path on the right, which is on University property. One area of disagreement: the railroad wanted to maintain the mineral rights on its property. I doubt they were expecting to find gold or silver in southeast Minneapolis. Still, it makes you wonder. What’s under there?

I like the back roads look of the Dinkytown Trench, so I got on my bike and shot photos of the bikeway as it appears today. My tour starts on Fifth Street. TCF Stadium is just behind me in the photo below.

The route leaves Fifth Street and follows this grassy strip toward the railroad yards.

Then it runs beneath several Dinkytown bridges. That’s downtown Minneapolis in the background.

In case you’re completely flummoxed about where this trail is, here’s a well-known Dinkytown landmark from below.

We’re getting close to the end. The route veers left, hugging the wall,

offering bicyclists a great view of the scenic coal-handling facility (white building on the right) on the U of M east bank campus. West bank buildings are in the background, and the Mississippi is coming right up.

Ta-da! Bridge Number 9 over the Mississippi River. No bicyclists in this photo.

The U of M Bikeway will be a new link in the city’s extensive bike trail network,  and will make my secret bridge, Bridge Number 9, much less secret. But the city of Minneapolis has long had plans to “out” this bridge. Bicyclists will soon be able to ride on paved trails from south Minneapolis to the St. Paul campus without ever worrying about a big truck flattening them. That’s a good thing.

It sounds as though the hardest part of planning this bike path is over. Now we wait for the surveyors to survey and the winter to wear itself out. And then I’ll have to start sharing Bridge Number 9.






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Beaver building a house — live action!

The list of those who work the Mississippi River as it flows through Minneapolis is much shorter today than it used to be. Fewer tugboat captains, fewer deckhands. But beavers, those riparian workaholics, are still at it.

I first saw them a few years ago in the east channel of the Mississippi River near Nicollet Island. A whole family: mom, dad, a few beaverettes. They seemed to be living in a slightly ramshackle house of sticks on the shore, but the whole thing washed away in high water the next year.

Well, they’re back. Or at least one of them is. And here’s the house he’s working on.

A few mornings ago, he was hauling sticks. I’m not sure whether he was adding sticks to his house or stashing them away for winter food. But he did all this stick-hauling just below Main Street, near the Japanese restaurant Kikugawa and the newly-relocated Wilde Roast Cafe. On shore there was much less activity — an occasional runner, an occasional car. Fairly quiet at 6 in the morning.

Beavers are nocturnal and I’ve never seen this guy in the afternoon. Maybe his night shift was ending and he was hauling his last stick. At any rate, I felt lucky to get video of this rather large rodent going about his work.

American beavers were nearly wiped out in the 1800s by international demand for beaver felt hats, but these days we go hatless as we discover how these big rodents help create wetlands and improve the quality of waterways. Odd to think of rodents being a sign of a healthy waterway.

And speaking of that, a few days earlier I saw a series of small oil slicks traveling downstream on the same spot of the river. When I called the city’s help line (311), the dispatcher said, Oh yeah, we get that sometimes.

We do?

I didn’t mention the beaver. I wasn’t sure an oil slick dispatcher person would necessarily care about a beaver building a house in the middle of the city — against all odds — and therefore we shouldn’t spill oil. The dispatcher did say he would send someone out to take a look. I hope he did.

By the way, I don’t think our downtown beaver is building a new dam on the Mississippi — just a house, and kind of a small one at that.

One last photo: the beaver house is just off the frame to the left, but you can just see the log that he swam past, and in the background, the Third Avenue Bridge. It will be a peaceful place in the winter to hang out and chew sticks.

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Borrowed scenery: two clocks

I consider any and all scenery on the west bank of the Mississippi River to be “borrowed scenery” for those of us on the east bank. The term comes from Japanese gardeners, and it refers to the idea of including background features, such as trees and mountains, into the overall composition of the garden.

The moon is part of my borrowed scenery.

A year ago, the full moon was setting as I was taking an early-morning walk across the Mississippi River. Its round face mimicked the moon-shaped clock on the Federal Reserve Bank Building at the west end of the Hennepin Avenue bridge.

When I hauled the camera along a few months later, the moon, with its confusing rhythms, set in a totally different spot. It was nowhere near the Federal Reserve clock. So I had to wait for it to come around on the guitar, as Arlo Guthrie famously puts it when he sings Alice’s Restaurant. It finally came around this past weekend.

The time on the Federal Reserve Bank clock was accurate. The moon is also a reliable timekeeper, but nearly useless for most of us. Ask anyone on the street to explain the phases of the moon or why it’s sometimes high and sometimes low in the sky, and most of us will go blank.

In this yearlong wait for the moon to come around again, I have learned that each phase of the moon is high or low on its own seasonal rhythm. The rhythms are so confusing, even migrating birds prefer to rely on the sun for navigation.

Here’s another view that includes the top of one of the bridge’s suspension towers.

Last week, the president of the Federal Reserve Bank in Minneapolis was in the news. He opposed the Fed’s decision to keep interest rates really, really low for two more years. He felt so strongly, he even put up a video explaining why. Behind him you can see the bulky bridge suspension towers (but no moon).

The Fed’s clock is ticking on that two-year promise and the moon will keep time along with it. Look for the full moon a couple of Augusts from now as it sidles up to the Fed clock early in the morning. Interest rates might be rising just as the moon is setting.

Thanks heaps to Dave, serious student of the moon and trusty carrier of tripods.




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What’s blooming in the urban prairie patch?

Almost every day, I get a tiny dose of prairie  in the middle of the city. The Sixth Avenue Greenway, just a few blocks from the Mississippi River, looks a little unruly and neglected this time of year, but it’s also bursting with prairie flowers.

I photographed some of them this week in their gritty urban contexts:

Purple coneflower and utility pole

A sunny sunflower blooms across the street from the neighborhood carbon steel tubing supplier, Metal-Matic:

Sunflower and semi -- two bursts of color

Milkweed and smokestacks? Both have vertical presence, but otherwise not much in common:

Two pairs of stacks -- milkweed and smoke

I used to grow butterfly weed in a backyard prairie garden in St. Paul. It’s one of my favorites. Here it seems especially plucky, sprouting out of an old parking lot:

Butterfly weed on crumbling asphalt

As I blithely pass by, hoary vervain is busy attracting insects like bees and butterflies. An Illinois wildflower website lists the insects that go for hoary vervain in their state — long-tongued bees such as little carpenter bees, cuckoo bees, miner bees, and large leaf-cutting bees, plus green metallic bees, thread-waisted wasps, bee flies, thick-headed flies, butterflies, and skippers. Wow. I wonder if I have ever seen a cuckoo bee.

Candelabras of hoary vervain brighten up the sidewalk

Black-eyed susans, everyone loves. And behind them stands one of the trademark Marcy-Holmes neighborhood miniature bronze sculptures:

Pioneers probably dug up black-eyed susans to build this house

Purple prairie clover has escaped the greenway and established itself on the ‘wrong’ side of the sidewalk. The flowers will most likely vanish if the proposed apartment complex goes up on the corner of Main Street and Sixth Avenue SE. Maybe the developer could consider establishing another prairie patch nearby.

Purple prairie clover pointing little purple fingers at the developer's truck behind them

If prairie grasses can be adorable, side-oats grama is. Its flower clusters line up on one side like flags on a pole.

Side-oats grama grass reaching over the sidewalk

I don’t know if this patch of big bluestem grass at the Soap Factory art gallery (around the corner from the Sixth Avenue Greenway) was planted or if it arrived accidentally. But it’s great, and if I squint, I can pretend I’m on a windswept tallgrass prairie in western Minnesota. Back in the 1800s, energetic farmers plowed under most of the tall grasses in order to plant crops, but now we’re planting prairie grasses again in prairie restorations. My favorites are at Afton State Park and the park reserves in the Three Rivers Park District.

Big bluestem, a Little House on the Prairie grass



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Why don’t the oil and gas drillers want our sand?

Several feet beneath me (and you, too, if you live in Minneapolis or St. Paul) is a thick layer of sugar-like sand — about a hundred and fifty feet thick. Here’s a tiny slice of it:

Photo by Mark Ryan, Science Buzz blog, Science Museum of Minnesota

It’s the St. Peter Sandstone, and the sand grains are 99 percent quartz.

St. Peter Sandstone

The grains are also quite small, too small to be useful in society’s latest effort to pull every last molecule of oil and gas from the ground.

That effort is called fracking. The word comes from the term hydraulic fracturing. If you haven’t heard of it, well, it’s probably time.

All over the country, oil and gas companies are now cracking, or fracturing, rock that used to be considered too tight or compressed to release its trapped treasure. In the fracking process, drillers inject a stew of water, chemicals and sand into the rock, which fractures it and creates pathways for the oil or gas to reach the well. The role of the sand is to help hold those tiny cracks open. This video does a great job of showing you the whole process.

So, why doesn’t the energy industry want our sand?

We can thank — or blame, depending on your point of view — about four million years of Paleozoic wind-blowing and wave-crashing.

Here’s the story behind the St. Peter Sandstone:

Once upon a time (early Paleozoic, about 450 million years ago), it was warmer and wetter than it is today, and not only that, our continent straddled the equator. There was a lot of life in the sea, but not much on land, maybe some single-celled stuff, just peach-fuzz. It’s hard for me to imagine that part.

In this warm, wet climate the sea covered much of the mid-section of the United States, including southern Minnesota. The exposed part of the continent wore down over the years, as continents do, and the sediments washed into the shallow sea.

The sand-sized particles (the ones we’re interested in) came to rest along the edge of this massive sea and formed things like beaches and tidal flats. The sand was tossed around by the tides and waves and wind for a long, long time.

As a result, the quartz grains in our sand are well-rounded, well-worn, frosted, scuffed…in other words, beat up. With all this knocking around, the grains got smaller and smaller, a fraction of a millimeter across.

Micro-photograph by M. Dittes and J. F. Labuz, University of Minnesota

The oil and gas drillers like their sand grains bigger, all the better to keep those cracks in the rock wide open. That’s why they don’t like our sand.

Elsewhere in Minnesota and Wisconsin, things are different. Oil and gas companies are finding just the right sand deposits and are removing entire hills from the rolling hills of Wisconsin. The StarTribune has written about the relatively new phenomenon. Many others have written about fracking, too, including the New York Times and the Wall Street Journal.

Even if our sand were just right for fracking, we probably aren’t desperate enough for fossil fuels to agree to a massive sand quarry in the middle of Minneapolis.

Are we?

I, for one, am grateful that our sand grains are too fine for fracking. But the whole issue is a pesky reminder that we Midwesterners can’t look at distant oil spills and then hop in our cars and say, Whew! Somebody else’s problem!

Thanks to many people for help with this post: Tony Runkel, Richard Lively, John Mossler, and Robert Tipping — all with the Minnesota Geological Survey, and Chris Paola, University of Minnesota.


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How Bridge 9 holds it together

When I moved to the Minneapolis riverfront, I wanted to learn about the bridges. This stretch of the Mississippi River has so many of them. A week and a half after we unloaded the moving truck, the 35W bridge — a few blocks from our new home — collapsed. My desire to study bridges collapsed along with it.

But four years have passed. The memorial to the victims is finally under construction. I think I’m ready to dabble in bridges.

No better place to start than Northern Pacific Bridge No. 9, my favorite Minneapolis bridge, and the bridge featured at the top of this page. The first thing I learned was that the former railroad bridge near the University of Minnesota was called a deck truss bridge. A deck what?

Second word first. Truss. To oversimplify it, a bridge truss is just a pattern of interconnected triangles. It’s built of diagonal, vertical and horizontal elements (all performing different structural roles, but no physics here), and in the case of Bridge 9, the elements are made of metal, probably steel.

The deck is laid on top of the truss. As I walk, bicycle or dawdle across the bridge, I can’t see the truss as it does all the hard work of supporting the deck, defying gravity and keeping me out of the river.

The geometric maze of metal beneath the deck of Bridge 9 is actually two mazes. I had read this, and I had been told this by various people including Denis Gardner, a Minnesota bridge historian. Still, I looked at the bridge and I saw…a maze.

The best way to distinguish one maze, or web, from another is to look at how the metal pieces are connected. Some of the pieces, or members, are connected with pins.

Pinned connection on Bridge 9

Here’s another look at the same thing:

The pin-connected truss was built almost 125 years ago. Pinned connections were the height of bridge engineering at the time.

Other metal members of Bridge 9 are riveted together.

Riveted connections were stronger and more rigid than pinned connections, which allowed some movement. The Northern Pacific Railroad added the stronger web to Bridge 9 about ninety years ago so that the bridge could carry heavier trains.

The plate with all the rivets is called a gusset plate, and that term should ring a bell. The old 35W bridge was also a deck truss bridge. Its wimpy gusset plates sat like a 300-pound gorilla in the middle of the investigation following the 35W bridge collapse.

Bridge 9 carries pedestrians and bicyclists now. Its pins, rivets, and plates are probably strong enough to support such a light load, at least, I hope so.

Here’s a look at both types of connections. The light and spidery webs (with pins) are on the outside, the chunkier truss (with rivets and plates) is between them.

Bridge 9 holds itself together in more than one way, and that’s probably a good model for the rest of us.

If you’re interested in bridges, especially old bridges, I recommend Denis Gardner’s book, Wood, Concrete, Stone, and Steel: Minnesota’s Historic Bridges. It’s highly readable and full of photos of charming old bridges.

I thank Denis for taking the time to answer so many of my bridge questions.

I’ll leave you with a three-bridge photo. The view is looking downstream on the Mississippi River — first a curved pier of the new 35W bridge, then a concrete arch of the 10th Avenue Bridge, and finally the rusty webs of Bridge 9.

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Didn’t see any Lycra on this year’s underwear bicycle riders

Thank goodness I didn’t miss the annual Fourth of July Underwear Ride sponsored by mplsbikelove. It’s the single best reason to stay in town over the Fourth. Yes, the fireworks are cool, but the underwear bicycle ride just plain makes you laugh.

If I’m correct, the ride has international origins with a more serious tone. World Naked Bike Ride encourages people around the world to strip down to protest “indecent exposure to vehicle emissions.” People in almost fifty U.S. cities have participated at one time or another.

Thousands of lunatic bicycle riders participate in Portland.  In Boulder, CO, the police have gotten downright cranky about it.

As you’ll see from my photos, the Minneapolis riders don’t strip down completely. Maybe they don’t trust the weather, and I wouldn’t blame them. A freak snowstorm or a wall cloud could blow in at any time. Or maybe the riders just want to have fun, and goofy underwear tends to be a lot funnier than full frontal nudity. From my vantage point across the street, I couldn’t see any angry political protesting — just 150 or so happy riders waving and encouraging all onlookers to join them.

Here they are (and I don’t believe any of the young people in my immediate family are in these shots):

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Rickety-chimney chimney swifts

The Soap Factory‘s rickety chimney didn’t win my Rickety Chimney Contest but it probably should have.

Soap Factory with downtown Minneapolis in the background

It has a crack running down the length of it and it’s been hit by lightning a couple of times, according to Ben Heywood, the art gallery’s executive director. He says they plan to repair the chimney. Good idea except for one thing:

Chimney swifts live in it. During the day, they launch themselves out of the chimney like miniature missiles, then they zip around and around in the sky above the chimney, catch bugs, and generally have a great time. At twilight, they dive back into the chimney one or two at a time. The birds are non-stop entertainment.

I’ve tried to get a photo, or better yet, a video, of the Soap Factory chimney swifts. This is what I got:

Blank sky above Soap Factory chimney

Nothing but blue sky. The birds are small and fast. Someone else had more luck:

Houston Nature Examiner photo

Heywood knows the birds are in his chimney. He doesn’t know whether the swifts will like the chimney when it’s repaired. “What I know about chimney swifts is absolutely zero,” he says. What I know is only a bit more than that, but an Internet search shows that lots of other people around the country are repairing their rickety chimneys, and the chimney swift population is declining.

The Driftwood Wildlife Association suggests building towers, or surrogate chimneys, for the insect-loving birds. After all, we install boxes on tree trunks for wood ducks, bird houses in the middle of restored prairies for the bluebirds, why not build a tower for chimney swifts?

An added bonus: if you turn a Soap Factory artist loose with a chimney swift tower, it could become an art project.

A YouTube video of chimney swifts

Thanks to Ben Heywood, and I wish him luck with his rickety chimney. And thanks to Dave for identifying the chimney swifts, which I thought were swallows.

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