Joshua Holt said Saturday afternoon "thank you for the support, your prayers, and for never giving up and leaving us behind."
World War II Merchant Marine Duane Roy Dreher, 34 at the time, went missing from Mason City, Iowa on November 7, 1955. Three days later, his car was found abandoned at a nearby creek. He was never heard from again.
A Big Island tourism official says summer bookings are down 50 percent, thanks to fears over the eruption.
"We will remember him fondly as the great explorer who reached out to embrace the universe," NASA Administrator Jim Bridenstine said.
Ireland's Prime Minister described the result as the culmination of a "quiet revolution" in what was once one of Europe's most socially conservative countries.