Auxiliary material for
Long-lived explosive volcanism on Mercury
Rebecca J. Thomas1, David A. Rothery1, Susan J. Conway1 and Mahesh Anand1,2
1 Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA,
U.K.
2 Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, U.K.
Corresponding author: Rebecca J. Thomas, Department of Physical Sciences, The Open University,
Walton Hall, Milton Keynes, MK7 6AA, U.K. rebecca.thomas@open.ac.uk, +44 (0)1908 858535
Geophysical Research Letters, 2014
Introduction
We include an auxiliary figure and table showing the distribution of explosive volcanic landforms on
Mercury and seven figures consisting of images, cross-sections and crater-counts from two sites on
Mercury where there are thick pyroclastic deposits. These data were collected by examination of
images taken by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging
(MESSENGER) spacecraft and by the creation of DEMs using stereo imagery. Crater counting was
conducted using the CraterTools tool for ArcGIS. Details of the methods used are given in the main
body of the paper.
1. ts01.pdf (Table S1) Catalogue of endogenic pit groups with a surrounding spectral anomaly
and their host impact crater.
1.1 Column “Pit Group ID”, Pits are grouped on the basis of close (< 50 km) proximity
and/or occurrence in the same host crater.
1.2 Column “Central latitude”, decimal degrees, latitude of the centroid of the pit group.
1.3 Column “Central longitude”, decimal degrees, longitude of the centroid of the pit group.
1.4 Column “Crater degradation class”, degradation class of the host crater, suggesting an age
of (oldest to youngest): 5 = Pre-Tolsojan, 4 = Tolsojan, 3 = Calorian, 2 = Mansurian, 1 =
Kuiperian to late Mansurian, 0 = cannot be determined, n/a = does not lie within a crater.
1.5 Column “Crater name”, IAU name of the host crater, if named.
2. fs01.jpg (Figure S1) Distribution of endogenic pits with a surrounding relatively bright, red
spectral anomaly. Where the pit penetrates an impact crater, the degradation state of that
crater is used to color-code the site. This indicates the maximum age of pyroclastic activity.
The relative freshness of the crater indicates an age (youngest to oldest) in the Kuiperian to
late Mansurian (yellow), Mansurian (bright green), Calorian (dark green), Tolsojan (light
blue) or pre-Tolstojan (dark blue). Red dots: pits that are not superposed on an impact crater
or where the crater degradation state is unclear. Locations of Figures 1 and 2 indicated by
white rectangles. (Base image: global color mosaic v5, NASA/Johns Hopkins University
Applied Physics Laboratory/Carnegie Institution of Washington.)
3. fs02.jpg (Figure S2) Evidence for and dating of explosive volcanic activity at AP2 (-135.5° E,
-8.4° N). (a) A pit around the central peak of an impact crater is surrounded by relatively
bright and red deposits (colour composite combining images EW0262430050I,
EW0262430070G and EW0262430054F with panchromatic sharpening using image
EN0242378054M); (b) Areas sampled for crater-counting (blue: pyroclastic deposit, green:
nearby smooth plains), white box: extent of a and c, white lines: cross-sections in Figure S4
(Image: global monochrome mosaic v.9); (c) High-resolution monochrome image showing a
pit annular to the central peak of an old, degraded impact crater. White dashed outline: rim of
host crater, blue outline: area used for counting superposed impact craters; yellow open
circles: primary impact craters; red open circles: secondary impact craters. (Image
EN0242378054M) (Image credit: NASA/Johns Hopkins University Applied Physics
Laboratory/Carnegie Institution of Washington.)
4. fs03.png (Figure S3) Cumulative crater frequency plots showing that the model ages of
explosive activity at AP2 and nearby effusive activity are very similar. Red points: crater
counts for the surface of the AP2 deposit; red curved lines: fits to the AP2 deposit data; blue
crosses: crater counts for the surface of the nearby smooth plains; blue curved line: fit to the
smooth plains data; straight lines: error bars (AP2 deposit area: 7.27 x 102 km2; smooth plains
area: 3.31 x 104 km2). (a) Fits to craters in the ranges 800 m – 1.15 km diameter and 1.2 – 2
km diameter using the Neukum production and chronology function. A resurfacing correction
was applied to account from the exclusion of larger craters in these fits. Results of
randomness analysis (top) show that craters can be considered random for all diameters using
a mean closest two neighbours distance (MC2ND) measure and for diameters > 1 km using
the standard deviation of adjacent area (SDAA) measure; (b) Fits to the MPF.
5. fs04.png (Figure S4) DEM cross-sections across AP2 as indicated in Figure S2b. Mounds of
material up to > 360 m thick are observed around the pit margins. DEM derived from images
EN0242378054M and EN0257763833M.
6. fs05.png (Figure S5) Differential plot of crater frequency around AP2 showing two
populations of craters (ranges as in Figure S3), indicative of a resurfacing event.
7. fs06.jpg (Figure S6) Evidence for explosive volcanic activity north of the Rachmaninoff
basin. (a) Colour composite showing a large endogenic pit surrounded by a relatively bright
and red spectral anomaly and more spatially-limited thick, steep-edged deposits. White
rectangles: extent of b and c, white lines: cross-sections in Figure S8 (Images
EW0254942495I, EW0254942487G and EW0254942491F); (b) Monochrome image of the
area around the pit, showing that the pit is the most probable source of the high-relief material
to its south (excerpt from the global monochrome mosaic V9); (c) High-resolution
monochrome mosaic of the pit. Deposits around it superpose craters on the continuous ejecta
blanket of the Rachmaninoff basin (white arrows). Blue outlines: area sampled for cratercounting, yellow open circles: primary impact craters; red open circles: secondary impact
craters. (Images EN0239539037M and EN0239539024M) (Image credit: NASA/Johns
Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.)
8. fs07.png (Figure S7) Cumulative crater frequency plot showing resurfacing around N
Rachmaninoff. 1.2 - 2 km diameter craters give a model age of 3.6 Ga (+0.1/-0.1) and an
underabundance of craters 600 m – 1.1 km diameter indicates later resurfacing (Deposit
sample area: 1.41 x 103 km2). Randomness analysis (above) indicates that craters can be
considered random for crater diameters between 120 m and 1 km using a mean closest two
neighbours distance (MC2ND) measure and between 250 and 710 m using a standard
deviation of adjacent area (SDAA) measure. This indicates that it is reasonable to consider the
crater population used to obtain the younger model age statistically random.
9. fs08.png (Figure S8) DEM cross-sections across N Rachmaninoff pit as indicated in Figure
S4a. Large mounds of material at its west and south margins, and more subdued relief to its
north and east. DEM derived from images EW1003930329G and EW0254971314G.