Scientist need to decide which volcanoes in the united states they should monitor

enzymes loose their form in both unsuitable ph and temprature.

Explanation:

at very high tempratures enzyme molecules denatures due to high speed movements, at low tempratures enzymes works too slow to be useful enough.

low ph solotions contain lot of H+  and high ph solutions have few H+ , and the number of these H+ ions have polar effects on enzymes.  some Enzymes like pepsin works perfect in acidic environment ( ph=2)  while others might work at  high ph  or average ph( like Trypsin  works well at ph=7).