Why is the top of a canyon visible from the bottom during a rainy hike, but once at the top, the bottom is invisible because of the fog?

Question

During a rainy hike canyon walls are visible from the bottom (although a bit foggy). However, when I got to the top, I couldn’t see the bottom anymore—everything was just white. Can someone explain like I’m five why the top is visible from the bottom, but not the other way around?

Edit: missing detail, the weather didn’t change throughout the hike. An the Bailong Elevator led to the top so we reached it within a minute or so. When going down by a cable car the canyons became visible again.

In: Physics

Answer 1

There’s a couple factors.

First, we have to remember that *everything* you see is because light bounces off of it and into your eye. When you see an apple, it’s because light from the sun hits it, and the red light bounces off the apple and goes into your eye.

Also, your eyes adjust to the ambient brightness. Ever tried looking into a dark window on a sunny day? You have to shade your eyes to see anything inside, right? When you’re in the canyon, the sky and everything above is the brightest thing, so it’s easy to see clearly. When you’re outside the canyon, the bottom of the canyon is relatively much darker, so it’s already harder to see
clearly.

Another thing is to consider the path of the light. To see something outside the canyon, for example the canyon walls, from inside the mist at the bottom, you need light from the sun to bounce off of the rock, avoid the misty water particles, and then bounce into your eyes.

To see something inside the canyon from outside, you need light to come from the sun, avoid the mist, bounce off the bottom of the canyon, avoid the mist again, and bounce into your eyes. So it basically has to pass through the mist twice, giving it double the chance to get scattered or absorbed before it reaches your eyes.

Also, a lot of the light bounces *off* the mist particles. When you’re outside the canyon, the light bouncing off the mist can block the light bouncing off the bottom of the canyon, so you only see mist. When you’re inside the canyon, since the light is all coming from above, you don’t see much of the bounced light from the mist. All the light that reaches your eyes has basically passed through the mist, making the mist look mostly transparent.