Furthermore, this liquid aesthenosphere, which continues to create new crust at rifting zones such as the mid oceanic ridges, melts down subducting crust as the residue of this crust is drawn deeper into the mantle.
While volatiles trapped in the remaining crustal residue are ultimately assimilated into the mantle, lighter volatiles from the crustal melt are fractionated and float up towards the surface to feed plate margin volcanoes.
For example, the observatory in New Zealand, located somewhere along the 41 parallel, is within 250 km of Tanaki and the entire North Island active volcanic province.
Low pressure system centres approaching and high pressure system centres departing the Cook Strait will displace volcanic plumes from the North island to the South Island.
The same potential problem exists with the observatory at Alert in Northern Canada, because it is located inside the circumpolar wind zone along with the Arctic Rift and thousands of venting seamounts along key parts of the Northwest Passage.