Simplify the following text for a Grade 13 native English-speaking person.
Original: Volcanologists frequently visit volcanoes , especially active ones , to observe volcanic eruptions , collect eruptive products including tephra ( such as ash or pumice ) , rock and lava samples .
Simplified: Volcanologists visit volcanoes often , especially ones that are active , to look at volcanic eruptions , collect material from the eruptions , such as ash or pumice , rock and lava samples .