The Earth Impact Database

The Earth Impact Database comprises a list of confirmed impact structures from around the world. The database was conceived in its earliest form when a systematic search for impact craters was initiated in 1955 by the Dominion Observatory, Ottawa, under the direction of Dr. Carlyle S. Beals. This was achieved via the study of over 200,000 aerial photographs of the Canadian Shield. Since that time the list has grown as new craters have been added. When the Dominion Observatory impact group moved to the Geological Survey of Canada (GSC) in the late 1980s, a more formal listing was developed. In 2001, following termination of impact studies at the GSC, the database was transferred to the Planetary and Space Science Centre at the University of New Brunswick, Canada. The site is currently managed by John Spray (Director, Planetary and Space Science Centre). Major contributions to the development of earlier versions of this database have been made by colleagues Richard Grieve and James Whitehead. We would like users of this site to be aware of its purpose:

The Earth Impact Database is maintained as a not-for-profit source of information to assist the scientific, industrial, government and public communities around the world in furthering our collective knowledge of impact structures on Earth.

We rely heavily on the science community adding to the knowledge base, such that the list is kept as current as possible. In this light, the database is operated on consensus, relying on scientific input from the community at large. The database is thus a dynamic document, with new craters being added as evidence is collected.

The impact structure images have been compiled over many years. They are shown at relatively low resolution. Some images are available in higher resolution on request from the Data Manager. A small fee may be charged if the image is to be used for commercial purposes.

Criteria

The principal criteria for determining if a geological feature is an impact structure formed by the hypervelocity impact of a meteorite or comet are listed below. The criteria can be divided into megascopic (overview – bird’s eye / satellite scale), macroscopic (can be seen easily seen with the naked eye) and microscopic (requires a microscope to see) features, as follows:

1. Presence of shatter cones that are in situ (macroscopic evidence).
   
2. Presence of multiple planar deformation features (PDFs) in minerals within in situ lithologies (microscopic evidence).
   
3. Presence of high pressure mineral polymorphs within in situ lithologies (microscopic evidence and requiring proof via X-ray diffraction, etc.).
   
4. Morphometry. On other planetary bodies, such as the Moon and Mars, we rely on the shape of the impact structure to determine its presence and type (simple versus complex, etc.). This is a megascopic quality (i.e., too big to be seen unaided by the human eye, thus requiring remote sensing, aerial photography, detailed mapping of multiple outcrops to assemble and view the typically km- or multiple km-size structure). On Earth, recognizing impact structures solely by their morphometry is complicated by two factors: (a) weathering, erosion, burial processes and tectonic deformation can obscure and/or destroy the original shape; (b) certain terrestrial features generated by means other than impact can have comparable circular form (e.g., volcanoes, salt diapirs, glacigenic features), such that a circular structure alone is not sufficient to claim impact structure status. Some buried craters have been revealed solely by geophysical techniques, although drill core is typically required to reveal macro- and microscopic evidence to prove an impact origin.
   
5. Presence of an impact melt sheet and/or dikes, and impact melt breccias that were generated due to hypervelocity impact (macroscopic). These bodies typically have a crustal composition derived by the fusion of target rocks (i.e., there is no mantle contribution to the melt). Such melts may be contaminated by meteoritic (projectile) components (the latter requires specialized geochemical analysis to detect the projectile components). Melt sheets may be overlain by so-called fallback breccias (referred to as “suevite” by some workers), and material blasted out of the crater may form ejecta blankets about the original central cavity. For large impact events, ejecta can be distributed globally. Impact melt sheets are recognized by careful mapping and rock sampling followed by microscopy and geochemical analysis.
   
6. Pseudotachylyte and Breccias: Pseudotachylyte is a rock type generated by faulting at either microscopic or macroscopic scales. However, pseudotachylytes are also associated with seismic faulting due to endogenic processes (e.g., earthquakes due to isostatic rebound and plate tectonics), so they are not exclusively impact generated. However, in association with features listed above, they can be a contributory criterion. Pseudotachylyte associated with impact structures may form in radial and concentric fault systems that help to define the megascopic structure of the crater. Pseudotachylytes can be included in a family of rocks referred to as breccias. Many different types of breccia can be developed as part of the impact process (including impact melt breccias listed in (5) above), but breccias can also form by endogenic processes. The interpretation of breccias therefore requires considerable care and experience. Moreover, they should not be considered diagnostic of impact, but rather contributory evidence.

In terms of relative importance, it is generally considered that criteria 1-3 above are definitive (they all relate to the passage of a shock wave through rock and resulting modification processes), with contributory evidence being added by 4-6 (which result from secondary effects, such as gravitationally driven crater modification). For buried structures that cannot be directly accessed, but are well-preserved as revealed by detailed geophysical techniques (especially seismic data), some workers consider this as strong evidence in favour of an impact origin. Normally, buried craters are verified by drilling and sampling the material directly for evaluation using criteria 1-3 above.

Caveat

The Earth Impact Database represents a compilation of information from around the world. Maintaining this site is both a formidable task and a formidable responsibility. Moreover, it is a task that is growing because over the last 25 years the impact process has been increasingly appreciated by the Earth Sciences community as an important planet-building and planet-modifying process. A consequence of this is the exponential growth in publications relating to impact. For this reason, we require the cooperation of the geological community in maintaining this site. We ask that specialists notify us of developments relating to impact processes on Earth. Please inform us of relevant publications and abstracts so that we can strive to keep our files and website current. Send information to the attention of:

Data Manager
Planetary and Space Science Centre
Department of Geology
University of New Brunswick
2 Bailey Drive
Fredericton
New Brunswick E3B 5A3
Canada
Email: passc@unb.ca
Phone: (506) 453-3560
Fax: (506) 447-3004

 

Acknowledgements

We would like to thank the following institutions and individuals for their assistance by supplying imagery and information for the inventory over the last decade. Other submissions are acknowledged in the image captions.

• National Aeronautical and Space Administration
• European Space Agency
• Canadian Centre for Remote Sensing
• Intera
• J. Garvin, GSFC-NASA
• B. Ivanov, Institute for Dynamics of Geospheres
• P. Lambert, Sciences and Applications
• V. Masaitis, Karpinsky Geological Institute
• J. McHone, Arizona State University
• W. Reiff, Geological Survey of Baden-Württembur
• D. Roddy, United States Geological Survey
• C. Wood, University of North Dakota
• P.M. Vincent, Centre de Recherche Volcanique
• J. Stark, Continental Resources
• S. Gudlaugsson, University of Oslo
• F. Tsikalas, University of Oslo
• B.M. French, Smithsonian Institution
• D. Vaughn, Utah Automated Geographic Reference Center
• C. Roberto de Souza Filho, Unicamp
• A.P. Crosta, University of Campinas
• A.Y. Glikson, Australian National University

ASTER data was provided by NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

 

PASSC Director: John Spray
Data Manager

Last updated March 20, 2009

Site developed and maintained by
Planetary and Space Science Centre
University of New Brunswick
Fredericton, New Brunswick, Canada
Queries to: passc@unb.ca