Most ground-nesting bird species (Aleutian cackling goose, rock ptarmigan) and most burrow-nesting seabirds (storm-petrels, ancient murrelets, Cassin's auklets, tufted puffins) were extirpated by foxes; Semisopochnoi Island is currently in the early stages of recovery.

[2] Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains a caldera 8 km wide that formed as a result of the collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice.

Young, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

[3] A historic eruption of Semisopochnoi was reported in 1873, and at least four others may have occurred in the previous hundred years, but documentation is scant.

These eruptions apparently emanated from the flanks of Mount Young; the most recent flow appears to be less than a century old.

Cape St. Charles at 55° 37' West (-55.6167) on the Labrador Peninsula is the easternmost point of mainland North America.