A week has passed since a well-regarded poet disappeared on a Japanese island and his sister-in-law says the search will go on for at least one more day.

University of Wyoming professor Craig Arnold vanished April 27 while hiking up a volcano on a tiny island in the northern Ryukyu Islands of Japan.

Arnold has been traveling all over the world, working on a book about volcanoes.

His sister-in-law, Augusta Palmer of New York, said Monday that Japanese authorities have committed to look for Arnold through at least Tuesday. The search involves 20 to 30 people as well as search dogs and helicopters.

Japanese authorities say they've ruled out that Arnold is either inside the volcano caldera or at the barren top of the volcano.