Nothing in the scenery can cause this, it's surely a problem of your video settings. Most likely, a tweak you shouldn't have applied.
Try all the following:
- Reset your video driver to default
- If that doesn't work, try to delete your FSX.CFG, so a new one will be created with all default settings. Apply only the HIGHMEMFIX = 1 tweak and nothing else, if you use FSX.
- If that doesn't work, be sure you are not running the sim or any of the addons that starts with it in Compatibility mode.