A geologist is camped 4,876 m (about 3 miles) from a volcano as it erupts (a) How mche elapses before the geologist hears the sound from the eruption? (Assume the air temperature is 20°c.) (b) How much time does it take the seismic waves produced by the eruption to reach the geologist\'s camp, assuming the waves travel along the surface through granite as sound waves do? (Assume the granite temperature is 20°c.) Solution (a) Velocity of sound at 20 deg C, v = 343.2 m/s Now, d = vt => t = d / v given, d = 4876 m So, t = 4876 m / 343.2 m/s = 14.21 s (b) Velocity of seismic waves varies from v (seismic waves) = 1500 to 8000 m/s when you use v= 1500 m/s then, t = 4876 m / 1500 m/s = 3.25 s and when you use v = 1800 m/s - t = 4876 m / 8000 m/s = 0.61 s. .