How could further research expand on this initial study to provide a better understanding of the rock fall risk in Yosemite National Park?

Hi. You did not inform the survey that this question refers to, which makes it impossible for it to be answered. However, I will try to help you as best I can.

In general, a survey is expanded when the researcher repeats it with a larger sample, or with more variables, or with more plots, treatments and experimental units. An extended survey aims to present the results of the previous survey in a more comprehensive and complete way, revealing more complex problems and presenting more diversified conclusions. In that case, to answer your question, you should consider how the research presented can be modified to present more comprehensive results on rockfall hazards in Yosemite National Park.