The Emergency Management Office in the Northern Marianas is planning further helicopter missions to bring back full monitoring of the active volcano, Anatahan.
The seismic technician, Juan Takai Camacho, says he flew in with his team at the weekend, but only managed to restore one of the previous four seismic monitoring stations.
Mr Camacho says the volcano's ash plume forced them to take a low approach from the east.
"By approaching the island from five miles we started to close in, and also look for flying rocks, you know if there's a flying rock then we're not going to land."
Residents of Guam and the rest of the Northern Marianas chain are at risk from toxic ashfalls if the wind direction changes.
Mr Camacho says the mission was worth the expense and risk because of its benefit to public safety.