Satellite imagery from such resources as are cheap or free and it has now become standard archaeological practice to access such images and use them in archaeological survey

Answergoogle earth; i believe this is the correct answer, plz check first;

Answer they are produced by collision of tectonic plates;

Explosive eruptions are the most hazardous, involving large volumes of tephra and gases emitted from the volcano. lahars, pyroclastic flows, ashfall, and many other volcanic hazards are commonly associated with explosive eruptions. explosive eruptions are very dangerous. basically, any form of hazard can occur.