Okay kiddo, have you ever seen a volcano before? It's like a big mountain that spews out hot melted rock, or lava, from time to time. Well, when a volcano has bimodal volcanism it means that it doesn't always erupt in the same way.
Sometimes, it might have a really big explosion and throw out a lot of ash and gas. Other times, it might have a quieter eruption and just flow out some lava. It's like it has two different ways of doing things.
Scientists study bimodal volcanism because it can tell them a lot about how the volcano works and how it formed. They might look at the different kinds of rock that come out of the volcano during different eruptions or they might study how the volcano looks underground.
Basically, bimodal volcanism means that a volcano can change the way it erupts, and it can give us clues about how it works.