Strange Pattern on Van Tailgate: Investigating the Cause

[DaveC426913]

While driving to work today, a minivan in front of me had a strange pattern on its rear, the possible cause of which eludes me.

Van Tailgate

Edit: The sketch is, of course, an approximation. Actual line position and number may vary due to incomplete memory..

We've recently had a lot of snow, but now the temp has risen, and the snow is melting rapidly. It's been very foggy, and the today it's drizzling. All cars are covered in grime kicked up from dirt on the roads.

I'm almost sure this pattern is made of dirt/mud, but why it's laid out this way I can't imagine.

Those lines are mud-coloured (brown-black) no more than 1/8th inch wide, solid, (not broken), little variation in width with very well-defined edges. You can see one big strand across the middle that makes a continuous line across the tailgate and then the license plate and then the tailgate again. And you can see on the license plate where a piece appears to have broken away and slipped.

At first, I thought the rear of the van had been overgrown by a vine, and then when moved the vines tore away, leaving some strands. On second glance, it looked like the van had backed into cobwebs.

The most obvious answers:
- eddies from the moving van pushing water around
- melting ice slipping out of slots (such as the window sill) and sliding down the surface
but these would have left some sort of identifiable pattern.

Theories?

 

[brewnog]

Perhaps the van had been overgrown by a vine, and when the van moved the vines tore away, leaving some strands.

Alternatively, perhaps the van had been backed into some cobwebs?

 

[NateTG]

Do you have snowplows where you live?

 

[DaveC426913]

Do you have snowplows where you live?

Yes. You think that might contribute somehow?

 

[NateTG]

One possible answer is that there was a bunch of snow stuck on the car, and the run-off of the grime accumulated on the snow/no snow boundaries. In order to get the snow high enough on the van, it would probably have had to get in a snow berm.

Atlernatively, snow sliding down the van can leave clean tracks, but that's not what you're describing, and would not work nicely with the license plate.

Is this something you know the answer to, or something where you're looking for theory?

 

[DaveC426913]

It's b). I don't know what could possibly have caused this. Usually, emergent behaviour gives some indication as to the forces driving it. That's why I found it remarkable.

"One possible answer is that there was a bunch of snow stuck on the car, and the run-off of the grime accumulated on the snow/no snow boundaries."

I see where you're going, but that wouldn't explain why the boundaries have the same thickness regardless of the angle from vertical. yet they are all exactly the same thickness. You'd think it would look more like some sort of runoff pattern. Gravity seems to have little effect in this case.


Oh yeah, and it would have to be an awful high berm. I made sure I took note of the track above the window.

 

[NateTG]

How about:
The tailgate was opened up into something which left the tracks - like stuff stored above it in a garage?

 

[Integral]

Perhaps micro cracks in the finish give a gripping point for contaminants.

 

[Bartholomew]

A minivan would have a squarish back so that there wouldn't be smooth flow lines (too much turbulence), so it could have been the wind making that pattern.

Have you ever smacked wet clay onto a hard surface, and then pulled it back up? Is that the kind of pattern you're talking about?

 

[Janitor]

Dave's post reminds me of something. A room that my job takes me into at times has a strange phenomenon going on. The ceiling has two identical fans mounted on it. They both have the blades tilted the same way and to the same degree, and both can be made to turn at what looks like the same speed. Yet one blows air downward just as it is supposed to, and the other one blows essentially no air. I have pointed this out to at least four people. After they stand under each fan in turn, they say, "One of them must be pulling air up." Then I turn off the fans so that they can watch them spin down, such that they can verify that they are indeed turning in the same clock direction. I point that the paddle blades are not tilted in opposite ways. That is where they run out of ideas.

The only conceivable explanation I can come up with is that the ductwork that hangs down from the ceiling creates an unsymmetrical hydrodynamic environment for the two fans. But my intuition suggests that the ductwork should not be that dramatic in its effect on airflow under the fans.

 

[DaveC426913]

Perhaps micro cracks in the finish give a gripping point for contaminants.

The tailgate was opened up into something which left the tracks - like stuff stored above it in a garage?

It crosses the license plate too.

A minivan would have a squarish back so that there wouldn't be smooth flow lines (too much turbulence), so it could have been the wind making that pattern.

Too random. I mean, there's no pattern to the lines.

Have you ever smacked wet clay onto a hard surface, and then pulled it back up? Is that the kind of pattern you're talking about?

Yes, I know what you mean. That does closely match the layout of the lines. I'd say it's on the right path. But still, the lines shouldn't be so consistent in width.

 

[Moonbear]

What about splatter from another passing vehicle? Or, considering it's a minivan, there may have been little gremlins (a.k.a., children) at work, either finger painting or throwing mud and/or snowballs in the driveway

 

[DaveC426913]

Can you see any of those methods actually producing the effect shown?

 

[NateTG]

It crosses the license plate too.

Let's say that the tailgate is hinged on the side, for example, and get's opened into a bush. Then the mark left by the bush on the door would not really be interrupted by the license plate.

Of course, this is all idle speculation.

 

[RandallB]

What did you use to make your drawing ??

Maybe a thick cold dirty water splash. Like a moderern artist tossing buckets of paint. Only from a large splash out of scale with the car and the elements being cut up by a wind with some vortex in it to destroy any trackable pattern. Thick & sticky enough not to run and freeze quickly on car.

 

[tribdog]

maybe those strange marks were driving down the road with a strange pattern of ice and mud on it shaped like a minivan.
maybe the owner of the van was running late so couldn't iron out all the wrinkles
maybe someone on a motorcycle rearended the van

 

[quantumgenius]

I think it is more along the lines of a kid doing it
a motercycle as tribdog said or
a vine that was attached to the car and when the minivan moved the marks were made.

 

[tribdog]

it's tough to guess this one based on that drawing. If you can figure it out though maybe you can help me with this one: I have a stain on my shirt it looks like this . What caused it and how can I get rid of it.