spiking engine temp, dropping voltage?

Driving to work today and my engine temp cycled back and forth from 210 all the way up to the red band (but never into the red).

Then a few miles later, it sounded like the belt was squeaking, and my voltage dropped down to 9 volts.

And then the belt stopped squealing, voltage went back to 12 volts, but I still had the engine problem.

What is this?

At first I thought it was a bad thermostat, but now the belt noise makes me wonder if it's something else.

any ideas?

which seized, ripped up a belt, and messed up my day.

since the jeep is too far from home, now I get to pay somebody to fix it....wonderful.