JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109
 
PHOTO CAPTION                                MAGELLAN
                                             P-37789  MGN-37
                                             3/5/91
 
 
     This Magellan image is located in the Eistla Region of Venus
in the southern hemisphere and is centered at 5.5 degrees east
longitude, 18 degrees south latitude.  It is 122.8 kilometers (76.1
miles) across east-west and 107.5 kilometers (66.6 miles) across
north-south.  North is oriented towards the top of the image.  
 
     Shown in the image is an unusual volcanic edifice unlike all
others previously observed.  It is approximately  65.6 kilometers 
(40.7 miles) across at the base and has a relatively flat, slightly
concave summit 34.8 kilometers (21.6 miles) in diameter.  The sides
of the edifice are characterized by radiating ridges and valleys
that impart a fluted appearance to the construct.    
 
     To the west, the rim of the edifice appears to have been
breached by dark lava flows that emanated from a shallow summit pit
approximately 5.4 kilometers (3.3 miles) in diameter and traveled
west along a channel approximately 5.4 kilometers (3.3 miles) wide
and 26.8 kilometers (16.6 miles) long.  A series of coalescing,
collapsed pits 2-10 kilometers (1.2-6.2 miles) in diameter are
located 10 kilometers (6.2 miles) west of the summit rim.  
 
     The edifice and western pits are circumscribed by faint,
concentric lineaments up to 70.3 kilometers (43.6 miles) in
diameter.  A series of north-northwest-trending graben are
deflected eastwards around the edifice; the interplay of these
graben and the fluted rim of the edifice produce a distinctive
scalloped pattern in the image.  Several north-northwest-trending
lineaments cut directly across the summit region.  
 
     This peculiar volcanic construct is located 25-30 kilometers
(15.5-18.6 miles) north of Alpha Regio, a highly deformed region of
tessera terrain.  A collection of at least 6 similar volcanoes has
been observed near Thetis Regio, a region of tessera within
Aphrodite Terra.  Thus, these unusual  constructs tentatively
appear to be spatially associated with regions of tessera.  The
implications of this spatial association on the unusual morphology
of these constructs are being investigated.