WELLINGTON, New Zealand—The tsunami threat around the Pacific from a huge undersea volcanic eruption began to recede Sunday, but the massive ash cloud covering the tiny island nation of Tonga prevented surveillance flights from New Zealand to assess the extent of damage. Satellite images showed the spectacular eruption that took place Saturday evening, with a plume of ash, steam and gas rising like a mushroom above the blue Pacific waters. A sonic boom could be heard as far away as Alaska. In Tonga it sent tsunami waves crashing across the shore and people rushing to higher ground. The eruption cut the internet to Tonga, leaving friends and family members around the world anxiously trying to get in touch to figure out if there were any injuries. Even government websites and other official sources remained without updates on Sunday afternoon. New Zealand Prime Minister Jacinda Ardern said there had not yet …