13 February 2017

Q&A, episode 2

Posted by Callan Bentley

Time for another episode of “you ask the questions”… After posting a Google Form to allow anyone to submit questions anonymously last week, I got some excellent questions/topics submitted. I’ll try to get to a couple per week!

3. Why does the Massanutten Mountain not run the whole length of the Valley?

Some background: the questioner is asking about the mountain ridge system where I live: Massanutten Mountain and the Fort Valley. It is situated in the middle of the much larger Shenandoah Valley, a valley in a mountain in a valley. This is a question about geomorphic expression of the Valley & Ridge province of the Appalachian mountain belt.

So the question is why doesn’t this

Google Earth

…look like this?…

Google Earth, modified by me!


Basically, it boils down to how “deep” the Massanutten Formation dives into the Earth.

The Massanutten (Tuscarora equivalent: a big thick package of Silurian quartz sandstone) is a sheet of sedimentary rock. It is a ridge former because it’s dominated by quartz: a hard, chemically-stable mineral. In the Shenandoah Valley, it overlies the Martinsburg Formation, a mix of shale and graywacke sandstone. It is overlain by Devonian limestones and shales. Where the Martinsburg Formation crops out, it weathers away relatively rapidly, making a valley. The same is true for the Devonian limestones and shales. But where the Massanutten Formation crops out, it weathers away more slowly, leaving a ridge.

The strata of the Valley & Ridge are folded, and the base of the Massanutten Formation dives into the Earth at the mountain’s northeastern end and re-emerges at the southwestern end. It’s like the bottom of a canoe:

This is the situation with Massanutten, too:

Massanutten is doubly-plunging synclinorium: an overall canoe-shaped fold that plunges down and inward in the “bow” and in the “stern.”

The one spot where the base of the Massanutten blips up above the land surface is about 2/5 of the way along the range, at New Market Gap, where Route 211 crosses over:

But under the Fort Valley, the bottom of the Massanutten Formation is buried deep in the Earth, and everywhere else (surrounding the mountain east and west, north and south) in the Shenandoah Valley, the bottom of the Massanutten Formation is above the surface of the Earth – or rather, it was, prior to erosion. The “canoe” used to be longer, in other words, and it’s getting whittled away over time. As the differential weathering proceeds on the landscape, the gap at New Market Gap will enlarge, and the Massanutten Mountain system will shrink and shrivel. Eventually, the deepest part (under the central Fort Valley) will be exposed, as a lone ridge, and then it too will succumb to the forces of erosion.

Summary / short answer: Massanutten Mountain isn’t longer because the tough stuff it’s made of has been eroded away everywhere else.


4. When will man walk on the Sun?

This is not going to happen.

There are a couple of issues.

First up: humans cannot walk if they are too hot. The Sun is too hot. The ‘surface’ of the Sun is around ~10,000 °F. That’s about ~9,900 °F hotter than you can take. You’d die before you could take a single step, much less go for a walk. But let’s say you got over the big discrepancy between your comfortable temperature range and what the Sun has to offer. What then?

The Sun is 333,000 times more massive than the planet Earth. So think of how quickly you hit the ground when you trip and fall here on Earth. If you were to stand on the Sun, your mass would be the same, but because the Sun is so much more massive than Earth, the gravity there would be much, much, much much, much, much, much, much, much, much, much, much stronger. In fact, it would not be advisable to attempt to go and see if you could walk on the Sun, because you would pretty much never be able to get away again. So you should know going in, this is the last trip you’re ever going to take. Even if you reconciled yourself to that, your muscles are going to be far too weak to take a single step away from the surface of so massive an object.

And finally, there is the issue wouldn’t be a ‘ground’ equivalent to walk on. The Sun is a big ball of plasma, and I think you’d have a rough time walking on it. It’s not a solid. Now, the average density of the Sun is ~1.4, while Earth is ~5.5, and your body is ~1.0. So your body would be less dense than the Sun’s average, but don’t think that’s a guarantee of ‘floating’ in the uppermost solar plasma. The Sun is roiling with convection, which means that your average non-flammable, impervious, super-strong Joe who steps foot on the Sun is likely to be caught up in one of these convection cells, and quickly pushed toward one of the downwelling zones. Just as convection in a pint of Guinness can drag bubbles (of low density) downward, I wouldn’t count on your relatively low density to save you. Convection is another risk of attempting to walk on the Sun.

So, bottom line: this is not going to happen. Sorry!

Got a question to prompt a bit of discussion here? Use this Google Form to allow anyone to submit questions anonymously.