Here's why:

* Felsic and intermediate magmas are thick and viscous due to their high silica content. This means they don't flow easily and tend to pile up around the vent, creating a dome-like shape.

* Mafic magmas, on the other hand, are thin and fluid, leading to the formation of shield volcanoes or less steep cone-shaped volcanoes.

Examples of volcanoes that form lava domes:

* Mount St. Helens (USA)

* Mount Unzen (Japan)

* Soufrière Hills (Montserrat)

It's important to note that lava domes can also form within the craters of existing volcanoes, regardless of the volcano's overall type.