Photoshop is hogging my disk! Help!

Yesterday I was editing a gigantic Photoshop file (100,000 pixels by 2500 pixels) that I’d put 48 shots from my 8 megapixel camera into, by opening the shots 10-20 at a time, going into each one and doing a select all (splat A) and copy (splat C), closing the file in question, then going into the big file and doing a paste (splat V). Along the way I’d saved the big file a few times. Along the way I’d also done some experimenting with cropping the small jpegs, and the big file, although I’d ended up rolling back all the changes.

This morning I decided I needed to crop some files and overlay them on the big file. First thing I did was flatten the existing 48 layers on the big file. Then I opened up 10 of the jpegs, just as I had before. But when I attempted to crop one of the jpegs, I got a message that I was out of swap space. Actually, I got two popup messages. The first looks like an OS message:

Your startup disk is almost full.
You need to make more space available on your
startup disk by deleting files.
[ ] Do not warn me about this disk again

The second came from Photoshop:

Adobe Photoshop
Could not complete your request
because the scratch disks are full.

At this point, I tried a bunch of things. I exited Photoshop, I rebooted, and I started up Photoshop. I opened only one jpeg. I verified that Photoshop said that the file took up 21 megabytes in memory and there were 30+gigabytes of disk space free. Then I tried the crop tool. And I got the same popups. Before I dismissed them, sure enough “df” and “Activity Monitor” both verified that all 30+ gigabytes of disk were gone. Other tests with other files have given exactly the same results. Even if I resize the file to half the size (and it says it’s only taking up 6 megabytes in memory) it still consumes all the memory when I attempt to crop it.

Can anybody tell me what would make Photoshop suddenly change so that cropping a file should cause it to use over 1000 times as much disk space as the size of the original file?