Canyonlands!

Our AG pool was installed just over 2 yrs ago. The installer leveled the ground and had us get some masonry sand for the bottom. We noticed this year that under the pool looks like the Canyonlands!! All the dirt settles into the canyons and it is difficult to vacuum them. Is this a common thing to happen or did the installer not do things correctly? I can't tell if the canyons are caused from ground cracks under the pool or if the sand ran like rivers during times of heavy rain. I haven't noticed ground cracks other places around the property though we are officially in a drought. But, I can't figure out how the rain water would get under to pool to make the sand run. I am sure that we don't have leaks since we never lost any water this year.

Any thoughts??

Moles?????

Well, if you're in a drought, the ground under your pool will likely lose some moisture, what happens depends a lot on the makeup of your soil.
How deep are your canyons? If they're pretty shallow, I doubt it's moles since when their tunnels collapse, they leave about 4-6" deep canyons, 4-8 inches wide.
Moles like to create tunnels near the edge of a water source (pond/stream), working their way inland sometimes up to 100 feet, if your pool is close to a pond or such it could well be.
Likely, it is due to the earth drying and shrinking under the pool, your sand should not wash out from rain unless you have a hill coming down to the side of your pool that allows tons of water to rush at the pool, some of this water could work it's way under and do some damage, but it would not create mini streams from one side to the other (too much weight pushing down from above).

I don't think it is moles. We do have a mole in our front yard, but his trails are a good 8 in wide. The canyons are maybe an inch wide and an inch deep. The don't run the hole diameter of the pool. My guess is that it is ground cracks - or maybe the sand wasn't packed well under the liner. It really isn't causing a huge problem - just more work when cleaning it. We try not to stand too much on the bottom of the pool anyway. Well, it is closed for the season anyway so we will see what it looks like come spring.

sometimes, small lines develop - like you said, ground cracks, although unlikely, I'd be more tempted to say your sub soil wasn't perfectly compacted....

I have some canyonlands in my pool too, which was just put up this spring. And I hate to tell you, but I just had a leak guy out to dive the pool. He found 6 holes, which he said were caused by ants eating the liner from below. I'm now concerned that the canyons are caused by ant trails.:mad: