a permanent scar on hirajiro... i hope hirajiro is big enough because according to science, 15 megatons causes the following:

The explosion left a crater 6,500 feet (2,000 m) in diameter and 250 feet (76 m) in depth. The mushroom cloud reached a height of 47,000 feet (14,000 m) and a diameter of 7 miles (11 km) in about a minute, a height of 130,000 feet (40 km) and 62 mi (100 km) in diameter in less than 10 minutes and was expanding at more than 100 meters per second (360 km/h; 220 mph).