WELLINGTON, New Zealand—An undersea volcano erupted in spectacular fashion Saturday near the Pacific nation of Tonga, sending 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 on Sunday still anxiously trying to get in touch to figure out if there were any injuries and the extent of the damage. Even government websites and other official sources remained without any updates. Satellite images showed a huge eruption, 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. Tsunami advisories were issued for Hawaii, Alaska and the U.S. Pacific coast. The U.S. Geological Survey estimated the eruption caused the equivalent of magnitude 5.8 earthquake. Scientists said tsunamis generated by volcanoes rather than earthquakes are relatively rare. …