abbreviated extract of table explanation comments from:

Volcanic and Magmatic Features on Venus: A Global Survey

Larry S. Crumpler, Jayne C. Aubele, and James W. Head III
Geological Society of America Special Paper
(in preparation)

Data organization

The Magellan Volcano Catalog in the following pages lists the locations of individual volcanic and magmatic features to the nearest 0.5 degrees, together with dimensions, brief descriptions or comments, existing names, and an "MVC (Magellan Volcanic feature Catalog) Number" consisting of the latitude, longitude, and short abbreviation for the feature type. These are arranged by feature type in alphabetical ordering, starting with north latitudes and prime meridian for each feature.

Explanation of Conventions Used

Table columns

Feature Terminology. The feature type designations used here are informal. Some terms imply a geologic origin and other terms are non-genetic. The level of geological detail available from Magellan image data are such that many of the centers may be assigned with reasonable certainty to a broad class of relatively well-known geologic phenomena, such as volcanoes or calderas, and the need for generally non-genetic terminology is diminished. Further more detailed division of feature types is generally more non-genetic. For these and other reasons discussed below, informal terms used early in the Magellan mission, such as "anemone", have been replaced in our catalog with more descriptive terms such as "radially-patterned intermediate volcano".

In general several non-genetic terms for many large scale features originated during the analysis of Venera 15/16 image data because the resolution was such that the geologic origin of many large scale structures, such as coronae or arachnoids, was indeterminate. Similar informal terms were used early in the Magellan mission for many types of newly-identified morphological features. An attempt was made with some preliminary terms used by the Magellan team, to use Latin derivative terms, as was done successfully with tesserae earlier. Informal usage of Latin in addition to informal and colloquial terms in general impeded this approach and resulted in errors. For example, the term "nova" arose from the astronomical term for an exploding star, even though its original Latin sense ("new") has nothing to do with a stellate pattern. These and other problems are of the type that are sorted out with usage, but should be noted and avoided. Currently the term "corona" seems to be accepted, "arachnoid" is not favored but may have been in use long enough to continue, but the terms "nova" and "tick" are generally considered inappropriate and in need of replacement. Simple terms that readily characterize a feature are most convenient, and as a rule non-whimsical terms are more appropriate.

Locations/Catalog Accuracy. The data in this catalog were compiled by two people jointly verifying each identification, classification, and numerical entry and acting as a check of the other's observations. A second verification of locations was performed subsequent to completion of the catalog by three people. Every effort was thus made during compilation and editing to check and re-check the accuracy of identifications, locations, dimensions, and tabulation. In addition to providing a continual check of individual accuracy, the tandem survey also controlled excessive "drifts" in identification and interpretation criteria that often occur in efforts of this type requiring observations over an extended period by a single individual. However, as with any carefully assembled, large geophysical data set of this size and complexity, a certain low percentage (generally 5%) of transcription and related "mechanical" errors occurs can occur [for example, see discussion of Pacific intraplate seismicity map in Lay, 1991, EOS, 72, page 468 or Wysession et al., 1991]. Users might be alert for the few obvious errors. Commonly identified and corrected errors during the review process included latitudinal errors resulting from inversion of north or south (e.g., 15 degrees instead of -15 degrees), corresponding mis-interpolation from latitudinal scale label points (e.g., -20 degrees mis-read as 20 degrees and a feature 2 degrees north of that identified as being at 22 degrees instead of -18 degrees), multiplicative longitudinal shifts (e.g., 290 degrees instead of 190 degrees, or 180 degrees instead of 190 degrees), incorrect MVC numbers, and typographical errors in feature descriptions. Instances of these types of errors are few, but these examples are offered as keys to recovering the data from the most likely occurrences of errors of this type.

Another advantage that has resulted from limiting the initial survey analysis to two individuals has been an increased ability to reach agreements about definitions, identifications, and related problems during the actual survey. Although, the disadvantage of this approach might be that a wide range of individual interpretations and perspectives are not presented within the catalog, the advantage is that the Magellan Volcanic Feature Catalog is assembled with extreme attention to consistency. This consistency together with the descriptive comments for each feature should enable alternative definitions or divisions to be readily accommodated if desired.

Dimensions. All dimensions are diameters, unless otherwise noted, and are approximate. Lava channel dimensions represent the length of channels. The diameters of large volcanoes are measured to the distal edges of the radial lava flows of median length. Diameters of coronae and arachnoids represent the mean diameter of the most prominent concentric ring. The diameter of radial fracture centers or stellate patterns is the diameter defined by using the median fracture length; fractures which are continuations of longer rift or fracture belt trends are not considered in arriving at the value for the median length.

MVC#. Few features on Venus are named as yet. Consequently, for purposes of brief identification, we have assigned a Magellan Volcano Catalog number ("MVC#") to each feature. The MVC # is simply an abbreviated description of the latitude, longitude, and volcanic feature type for each entry.

C1-MIDR.#s Preliminary list of C1-MIDRs in which the feature appears. F-MIDR #s Preliminary list of F-MIDRs in which the feature appears. Entered Comments. All comments identify salient characteristics relevant to the location of individual features with respect to adjacent features, apparent radar characteristics ("bright" or "dark"), and any other information deemed pertinent to establishing unique or unusual properties of the feature(s) listed. Feature Names. Names assigned to individual features included in the catalog are those approved by the International Astronomical Union as of the time of this writing. In general, the only systematic attempt to assign names has been for craters and coronae. With the exception of two or three well-known and frequently used names such as Eve Corona and Heng-O Corona, preliminary names or suggested names which are not on the official IAU Venus nomenclature list are included in parentheses. In some cases the co-ordinates listed in the IAU list for a feature may differ from those judged from Magellan data as representing the center of a particular volcanic feature. IAU names for which no corresponding volcanic feature is identified have not been included. Where the co-ordinates of our list and the IAU list differ significantly, the assumed corresponding feature name is listed with a query ("?") symbol. Many existing IAU-named features have no apparent Magellan volcano counterpart.

Identification of feature types is here based largely on volcanic criteria and infrequently corresponds to a single IAU physiographic term (e.g., "patera" often includes arachnoids, calderas, and large volcanoes). We note also that we have found few features on Venus which correspond to the official definition of patera as originally described; the usage of this term as a type of elevated relief feature, in particular, a low volcanic shield or edifice as exemplified on Mars and previously applied on Venus, does not correspond to the original IAU definition which identifies it as a flat-floor, irregular-margined depression. Other classifications. Due to variations in assumed defining characteristics and differences in interpretation, many individual features may be assigned to different feature types by different authors. This column list other classifications that have been assigned to the same feature by other authors.

Abbreviations: The following abbreviations are used in the catalog headings. Words in quotation marks note the equivalent informal terminology used in early science reports.

AR = Arachnoid                        IV/SSD = Steep-Sided Dome ("pancake")
CO = Corona                           LC = Lava Channel
FF = Festoon Flow                     LF = Lava Flow, Lava Field
IV = Intermediate Volcano             LV = Large Volcano
IV/FD= Fluted Dome (scalloped dome;   SFC = Stellate Fracture Center
   "tick")                               ("nova")
IV/RP = Radially-Pattern volcano      SF = small Shield volcano Field

Supplementary table notes: A query symbol ("?") denotes some difficulty or uncertainty in classification due to characteristics of a particular feature which are unusual or gradational to another feature type. A number following a feature designation [for example IV/SD(4)], means that there are multiple features of this type occurring close together (within 0.5 degrees lat/long ).

Graphic Showing Histograms of the Total Volcanic and Magmatic Center Count

The Tabulated Data