03.12-P

Effects of Elevation on Ground Impact of Small Asteroids

M. Patrick Goda, Jack G. Hills (LANL)

We consider meteoroids that impact ground at elevations h above mean sea level where h = 0 to 5 km. Meteoroids lose less energy in the atmosphere as h increases, so their ground impact damage is greater. This effect is enhanced if the bolide fragments. As an example, an iron meteoroid of radius R = 10 m and velocity at infinity = 15 km/s impacts the ground with velocity 0 if h = 0 km, however 18 km/s if h = 5 km. Iron meteoroids of this size ( 10 m) lose most of their energy within 2-3 km after fragmentation. Larger iron meteoroids with R > 25 m require approximately a scale height ( 8 km) to lose most of their energy, which reduces the effect of h. drops by less than 1 km/s if h = 0-5 km for iron meteoroids with R > 25 m. In contrast, stony meteoroids exhibit the greatest difference in with h when 40-60 m for = 0-15 km/s. The radius of the impact crater produced by a meteoroid of a given type, and R increases with h. This dependence on h is very small for iron meteoroids with = 0-15 km/s and R > 25 m. For stony meteoroids with = 0-15 km/s and R = 40-100 m, increases with h more dramatically than for iron meteoroids. As an example, a stony meteoroid with R = 60 m and = 10 km/s produces a crater = 400 m at h = 0 and = 1.6 km at h = 5 km. Stony meteoroids with R = 60-80 m and = 0-15 km/s produce craters at h = 5 km with = 0.6-1.6 km larger than craters produced at h = 0. Iron meteoroids exhibit the greatest increase in if 10 km/sec and R = 5-10 m. The mean elevation of the continents above sea level is approximately 875 m, but areas such as the Tibetan Plateau and the North American Rocky Mountains have 875 m. It is clear that estimates of R based on must take into consideration the effects of h.