On September 5, 2019, about 1540 Alaska daylight time, a tundra tire and tailwheel-equipped Piper PA-18 Super Cub airplane, N5057Y, sustained substantial damage following a nose over while landing at Birchwood Airport (BCV), Chugiak, Alaska. The flight instructor and private pilot receiving instruction were not injured. The airplane was registered to a private individual and operated by the flight instructor, under the provisions of 14 Code of Federal Regulations Part 91 when the accident occurred. Visual meteorological conditions prevailed and no flight plan had been filed. The local area instructional flight departed BCV. According to the pilot receiving instruction, the instructor had taken control of the airplane to demonstrate a landing. After touchdown and during the landing roll on runway 20L, an 1,800 ft. long by 50 ft. wide gravel-covered site, the airplane nosed over sustaining substantial damage to the right lift strut and rudder. The flight instructor reported that he took control of the airplane to demonstrate a landing. He said that, during the landing rollout and after the tailwheel was down, he noticed the tail begin to rise. As the tail continued to rise, he asked the pilot receiving instruction "what are you doing?", and he responded "I don't know, what are you doing?" Both pilots indicated that they were not applying pressure on the heel brake pedals during the event. An inspection of the airplane, by the FAA, revealed no preaccident mechanical malfunctions or anomalies that would have precluded normal operation. The closest weather reporting facility is PABV. At 1556, a METAR from PABV was reporting in part: wind, 260° at 3 knots; visibility, 10 statute miles; sky condition, clear; temperature, 63° F; dew point 46° F; and an altimeter setting of 30.20 inches of mercury.