Complex sentence: As the edges of the meniscus freeze they create a small dam which allows the water to rise higher and as the water expands above the ice dam the edges freeze again forming another dam on top of the first one.
Split into simpler sentences: As the edges of the meniscus freeze they create a small dam which allows the water to rise higher. The water then expands above the ice dam and the edges freeze again forming another dam on top of the first one.