[10] Around 1903 he did his obligatory military service at Gardermoen, just north of Oslo, and here met Captain Gunnar Isachsen who greatly influenced him, and first inspired his interest in polar regions.

In 1909, Isachsen invited Holtedahl to join him in explorations of Spitsbergen as official geologist of the group.

He delivered a significant contribution, not only in Norway but also for large areas of the Arctic and Antarctic.

His first geological work dealt with the Oslo Rift in the Cambrosilurian period, and he was part of the 1909–11 expeditions to Svalbard.

[2] He was the doctoral advisor of Bjørn G. Andersen, whose subsequent works on Quaternary geology he greatly influenced.