Answer:
Geologic features that are often associated with volcanoes or volcanic areas include craters, calderas, volcanic vents, geysers, and hot springs. Depressions commonly found at the top of volcanoes are craters.
Answer:
Radioactive isotopes are unstable and will decay. ... The isotopes will decay into a stable isotope over time. Scientists can tell how old the rock was from looking at the radioactive isotope's half-life, which tells them how long it would take for there to be half the radioactive isotope and half the stable isotope.