When a volcano erupts, it typically affects the humans in the vicinity by covering their environment with ash and sometimes with lava, according to Oregon State University. In addition, some volcanoes produce pyroclastic flows that are deadly to anyone in their path.
Volcanic ash is dangerous for people to breathe, as it is hot and filled with toxic chemicals. As ash piles up on houses and other structures, the weight of it can cause those buildings to collapse. Because lava moves slowly, it generally does not pose immediate danger to people but is often extremely destructive to buildings and fields. A pyroclastic flow is a rush of hot air and ash that sometimes sweeps down from an erupting volcano to engulf anything in its path; people in the way of a pyroclastic flow will be killed.