- changed
- chemicals
- considered
- correlation
- crustal
- date
- decreases
- deep
- despite
- distinguishing
- earth
- enhance
- field
- gases
- geochemical
- heat
- heating
- helium
- helium_3
- indicator
- indigenous
- input
- investigations
- isotope
- isotopic
- management
- mantle
- marginally
- necessity
- occurred
- originate
- output
- overseas
- overviewed
- relating
- relatively
- released
- resource
- rock
- shallow
- sources
- steam
- sustainability
- system
- unexpected
- variations
- volcano
