MSH_Post1980 is a DEM generated using data from the Shuttle Radar Topography Mission (SRTM; 15 m resolution I think) and the MSH_Pre1980-Crater is a model of the difference between pre and post 1980 eruption. This file can be printed and nests in the crater so that you can visualize the volcano before and after the explosive eruption. The two files are scaled appropriately so that printing should allow a good fit between the two models.
The pre 1980 topography was generated using the DEM provided here:
https://www.usgs.gov/data/digital-elevation-model-mount-st-helens-washington-and-vicinity-prior-1980-eruption
The author marked this model as their own original creation.