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 tex2html_wrap_inline31 = 15 km/s impacts the ground with velocity tex2html_wrap_inline33 0 if h = 0 km, however tex2html_wrap_inline33 18 km/s if h = 5 km. Iron meteoroids of this size ( tex2html_wrap_inline41 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 ( tex2html_wrap_inline45 8 km) to lose most of their energy, which reduces the effect of h. tex2html_wrap_inline49 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 tex2html_wrap_inline49 with h when tex2html_wrap_inline41 40-60 m for tex2html_wrap_inline31 = 0-15 km/s. The radius of the impact crater tex2html_wrap_inline63 produced by a meteoroid of a given type, tex2html_wrap_inline31 and R increases with h. This dependence on h is very small for iron meteoroids with tex2html_wrap_inline31 = 0-15 km/s and R > 25 m. For stony meteoroids with tex2html_wrap_inline31 = 0-15 km/s and R = 40-100 m, tex2html_wrap_inline63 increases with h more dramatically than for iron meteoroids. As an example, a stony meteoroid with R = 60 m and tex2html_wrap_inline31 = 10 km/s produces a crater tex2html_wrap_inline63 = 400 m at h = 0 and tex2html_wrap_inline63 = 1.6 km at h = 5 km. Stony meteoroids with R = 60-80 m and tex2html_wrap_inline31 = 0-15 km/s produce craters at h = 5 km with tex2html_wrap_inline63 = 0.6-1.6 km larger than craters produced at h = 0. Iron meteoroids exhibit the greatest increase in tex2html_wrap_inline63 if tex2html_wrap_inline109 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 tex2html_wrap_inline113 875 m. It is clear that estimates of R based on tex2html_wrap_inline63 must take into consideration the effects of h.