Earlier studies have shown that the anomaly in geomagnetic variations in the vicinity of Alert at the north end of Ellesmere Island is compatible with a narrow band of induced electric currents flowing in a northeast–southwest direction in the earth's crust or upper mantle. The present analysis of magnetic recordings obtained at 11 sites in Ellesmere Island during 1967 indicates that the Alert anomaly extends to the southwest as far as Eureka, a distance of 475 km. The anomaly has its greatest effect at Alert, and its "strength" diminishes by a factor of 2 or 3, 225 km to the southwest. Its half-width up to this point is about 50 km. The anomalous zone curves to the west near Greely Fjord 300 km southwest of Alert and appears to broaden near Eureka. The path of the anomaly closely follows the structural trends of the near vertical, tightly-folded strata of the Franklinian geosyncline underlying the whole Lake Hazen Plateau region of northern Ellesmere Island. Evidence for the extension of the anomaly through Ellesmere Island includes the near reversal of Wiese vectors on opposite sides of the zone, the confinement of the horizontal magnetic variation and its polarization transverse to the direction of strike, and the large contrast between apparent resistivities observed inside and outside the zone.

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