Need help with project from evil science teacher

Hello my science teacher recently assigned my class with an assignment where we have to show erosion. It has to be a 3-d project and I may use whatever material I want to present it. I want to use cake, does anyone have any ideas of what I could do to...

show this? My requirments are listed below.
3-d erosion and weathering project
1st. This model must be a 3 dimensional representation of some kind of a landform shown in a pre-erosion/weathering state and a post-erosion/weathering state.

2nd. Each representation must be at least 6 in squared so together they will be no smaller than 12 in squared.

3rd. You may use any material you wish to do this project. Food, dirt, wood, play-doe, anything you have. Be creative and accurate I want to see that you really understand the process at work.
Example: mountain made of rice crispy treats, and a valley made of a cake. Or you could show a large plateau 1st and then show how the grand canyon was made for the 2nd one.

4th. The paper must be at least one page long, single space, 12 point font, and have two sources cited one of them can be your book. In the paper you need to be as accurate as you can in reference to your model. You will write about the before and after aspects of your model and all of the different process in play that will affect the model you choose to do.
Example: the paper you would write on a mountain that is made of granite that eroded and weathered to create a clay filled valley would be much different than a paper you would write on how creeping affects things on top of the soil and a slight slope.

5th. Be creative and have fun with this project. Make sure that the model you are building is accurate and the paper you write refers to the model. Be as detailed as you can on both the model and the paper. I don’t want mom or dad to go out and spend money on this. Use what you have if you can. Look at the rubric to see how I will be grading this project. 100 point will be for the project. 100 point will be for the paper you write.

My first instinct was to use soda on the cake, because it's pretty acidic and will wipe out parts of the cake like erosion...but I think that will make it mushy and gross...It might depend on the cake though. Try it out first with a thick cake, not a spongey one. Coke will fizz and hopefully make weird erosion spots. If not, scratch the cake idea lol.