Just a thought... find a good picture of a volcano spewing and one of a German Shepard guide dog leading someone. Enlarge them and post them on the board. Then I would start my speech with something like. We can turn this unfettered energy into this leashed energy to guide us into a new age.
I think that would get their attention and you can use analogies from the two pictures to guide your speech.
You need to compare geothermal energy to other sources (gas, coal, wind and solar) to indicate what advantages it has over them. Include negative views of geothermal energy with possible counterarguments. Can end your talk by leaving the choice up to your audience.
Possibly these articles might help with methods of communicating:
I hope this helps a little more. Thanks for asking.
If you need technical information that isn't on the Internet, post specific questions. I may be able to help since I worked in geopressured-geothermal energy for about 20 years (as a chemist but some of the other aspects of the technology rubbed off during the process). The geopresured-geothermal approach is a little different than straight geothermal energy and it has its own disadvantages, primarily keeping corrosion down from the brine wells. And it isn't economical as long as natural gas is selling for the prices we see now.