Holden Crater Megabreccia: A Telltale Sign of a Sudden and Violent Event
NASA/JPL/University of Arizona
Holden Crater Megabreccia: A Telltale Sign of a Sudden and Violent Event
PSP_001666_1530  Science Theme: Impact Processes
Italian 

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This HiRISE image covers the southwest portion of the terraces and floor of Holden Crater situated in southwest Margaritifer Terra.

Breccia is a rock typically consisting of rock fragments of various sizes and shapes that have been broken, tumbled and cemented together in sudden geologic event (e.g., a landslide, a flashflood or even an impact-cratering event). If it were not for the dark sandy dunes dispersed throughout, this image could easily fool an expert into thinking that this image is actually a photograph of a hand sample of an impact breccia.

The prefix "mega" implies that the breccia consists of clasts, or rock fragments, that are typically bigger than a large house or a building. The rectangular megaclast near the center of the image is a colossal 50 x 25 meters (approximately 150 X 75 feet). The crater likely experienced extensive modification by running water, which is supported by observations of drainage and deposition into the crater from a large channel (Uzboi Valles) breaching Holden's southwest rim.

While it is possible that the megabreccia formed from a catastrophic release of water into the crater, a more likely possibility is that it formed from the impact that created the approximately 150 kilometer-in-diameter Holden Crater. Popigai Crater, a terrestrial crater of half the size of Holden, possesses a similar occurrence of megabreccia with a comparable range in megaclast size to the Holden Crater example.

An impact-generated megabreccia deposit, as observed in terrestrial craters, typically lies beneath the crater floor, so the exhumation of the megabreccia may be the result of down-cutting and erosion of water that once flowed through Uzboi Valles.

Written by: Livio Tornabene   (16 December 2009)

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Acquisition date
04 December 2006

Local Mars time:
15:41

Latitude (centered)
-26.828°

Longitude (East)
325.265°

Range to target site
260.1 km (162.5 miles)

Original image scale range
26.0 cm/pixel (with 1 x 1 binning) so objects ~78 cm across are resolved

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25 cm/pixel and North is up

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Equirectangular

Emission angle:
7.4°

Phase angle:
62.0°

Solar incidence angle
68°, with the Sun about 22° above the horizon

Solar longitude
145.1°, Northern Summer

North azimuth:
97°

Sub-solar azimuth:
36.8°
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Postscript
For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona. The image data were processed using the U.S. Geological Survey’s ISIS3 software.