Could Admiral Bryd's Journal be a hoax?

For those that don't know, Admiral Byrd made multiple expeditions to Antarctica between the 1920's and 1950's. While exploring there, he wrote in his dairy that he saw a UFO and a hole in the ice big enough to fit an airplane.

This hole was believed to lead to another civilization within the earth. But if there really was a hole, why not take a picture of it? They have a pictures of a penguins, but not a picture of a gigantic hole in the ground? Fishy...