Main Nav Gets Blocked When Scrolling

I couldn’t find a better way to explain this in the title but I’m having trouble with several plug-ins on the Twenty Fourteen theme. On some pages, my main navigation ends up in the background with the main page elements covering the navigation dropdowns. Best to take a look at my site as the issue is very clear on this page: https://www.w6ek.org/media/mediagallery

Load that page and then click on the “Activities” drop-down and you’ll instantly see what I’m talking about.

The page I need help with: [log in to see the link]