You could just shut off the source of the EMF to stop it.
Or if you are really afraid of the waves you can wear a Faraday cage suit. People use them for live performances with high voltage.
Lastly, you do not need to fear microwave band radiation, unless it is very powerful such as from a cell tower at point blank range, as it can cook you alive. It is not ionizing radiation, which means it cannot penetrate your skin unless it is a very powerful and close range wave.
It was 10 megatons of explosive force, definitely enough to set off the volcano, if you see the smoke plume you can see what looks like normal volcano eruption ash plume mixed with a large mushroom cloud, as if a nuke and a volcano were both exploded, which could also be why you hear a few smaller explosions first, and then the big mushroom cloud boom after those.
Very powerful antenna transmitting next to your head may not be the best idea. Especially if you have cell turned on you get a lot of radiation.