Answer: Fossil (Deposit)
Step-by-step explanation:
Determining the age of recent volcanic eruptions depends on deposits produced by ancient eruptions.
This deposits are trapped in lahars, volcanic ash fall, or lava flows from previous eruptions and will be used to determine the relative age of recent volcanic eruptions.
However, since human and volcanoes have long lifetimes relationship, this is an important tool for this research by establishing a forensic evaluation on the fossils. Then, a radiometric age dating of the deposits is incorporated and the past frequency of events can be determined (hence, providing the characters of the eruption and time it occurred).
Geologists with the information gathered can also make future occurrence predictions or forecasts of a volcanic eruption in the geographic area.