Abstract:
Small impact events recorded on the surface of Earth are significantly underrepresented based on expected magnitude-frequency relations. We report the discovery of a 36-m-diameter late Holocene impact crater located in a forested area near the town of Whitecourt, Alberta, Canada. Although undetectable using visible imagery, the presence of the crater is revealed using a bare-Earth digital elevation model obtained through airborne light detection and ranging (LiDAR). The target material comprises deglacial Quaternary sediments, with impact ejecta burying a late Holocene soil dated to ca. 1100 14C yr B.P. Most of the 74 iron meteorites (0.1–1196 g) recovered have an angular exterior morphology. These meteorites were buried at depths <25 cm and are interpreted to result from fragmentation of the original projectile mass, either at low altitude or during the impact event. Impact of the main mass formed the simple bowl-shaped impact structure associated with an ejecta blanket and crater fill. The increasing availability of LiDAR data for many terrestrial surfaces will serve as a useful tool in the discovery of additional small impact features.Herd C, Froese D, Walton E, Kofman R, Herd E, et al. (2008) Anatomy of a young impact event in central Alberta, Canada: Prospects for the missing Holocene impact record. Geology: Vol. 36, No. 12 pp. 955–958
I ♥ LIDAR!
Access: The Hart Mountain Antelope Refuge Road runs right by this larger circle site within the Harney Basin near the Warner Mountains in the South East corner of Oregon. The area is grassland with a desert mix.
The largest circle is over 2,000 feet wide and appears to be a spiral shape. The smaller spiral can be seen faintly to the SW and it's over 1,000 feet wide.
“The target material comprises deglacial Quaternary sediments, with impact ejecta burying a late Holocene soil dated to ca. 1100 14C yr B.P.”
BP= Before Present, but you need to calibrate Present as it changes every year. So the origin is normally set to 1950. That would indicate that the impact was around 1950 - 1100 = around the year A.D. 850. (and not around 2008- 1100)
I checked the Chronicle http://omacl.org/Anglo/part2.html It has no record of extreme weather etc at around 850.