page_title: Scalloped margin dome
hierarchical_section_title: Scalloped margin dome
caption_attribution_description: This Magellan image is of an area located in the Eistla Region [Error: This is in the Alpha Regio[1]] of Venus in the southern hemisphere and is centered at 5.5 degrees east longitude, 18 degrees south latitude. It is 122 kilometers (76 miles) across east to west and 107 kilometers (66 miles) north to south. North is at the top of the image. Shown is an unusual volcanic edifice unlike all others previously observed. It is approximately 66 kilometers (41 miles) across at the base and has a relatively flat, slightly concave summit 35 kilometers (22 miles) in diameter. The sides of the edifice are characterized by radiating ridges and valleys that impart a fluted appearance. To the west, the rim of the structure appears to have been breached by dark lava flows that emanated from a shallow summit pit approximately 5 kilometers (3 miles) in diameter and traveled west along a channel approximately 5 kilometers wide and 27 kilometers (17 miles) long. A series of coalescing, collapsed pits 2 to 10 kilometers (1.2 to 6.2 miles) in diameter are located 10 kilometers (6 miles) west of the summit. The edifice and western pits are circumscribed by faint, concentric lineaments up to 70 kilometers (43 miles) in diameter. A series of north northwest trending graben are deflected eastward 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 to 30 kilometers (15 to 19 miles) north of Alpha Regio, a highly deformed region of tessera terrain. A collection of at least six 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. A tessera is a complex, deformed terrain on Venus consisting of at least two sets of intersecting ridges and troughs. The implications of this spatial association on the unusual morphology of these constructs are being investigated.
context_page_description: A scalloped margin dome is a type of volcanic dome, found on Venus, that has experienced collapse and mass wasting such as landslides on its perimeter. The margins of these domes have arcuate headscarps or 'scallops' separated by ridges that are a consequence of adjoining scallops. Sometimes debris or slumping can be found at the bottom of these scarps or scattered many tens of kilometers away. Many examples show no debris at all. The center of these domes is often, but not always, a depression. There is another theory that the radial ridges of scalloped margin domes are volcanic dikes.
  During the first month of data from the Magellan spacecraft, the first of these features was found to the northeast of Alpha Regio, on Venus. It was one of the largest of these domes and therefore stood out. The strange feature was originally dubbed by the Magellan Project Science Team The Tick, because the many radiating ridges resembled the legs of a tick. Its concavity was likely confused as domelike as a tick's body, instead of the actuality which is that it is a bowl-shaped depression.
context_section_description: A scalloped margin dome is a type of volcanic dome, found on Venus, that has experienced collapse and mass wasting such as landslides on its perimeter.  The margins of these domes have arcuate headscarps or 'scallops' separated by ridges that are a consequence of adjoining scallops.  Sometimes debris or slumping can be found at the bottom of these scarps or scattered many tens of kilometers away. Many examples show no debris at all. The center of these domes is often, but not always, a depression. There is another theory that the radial ridges of scalloped margin domes are volcanic dikes.
  During the first month of data from the Magellan spacecraft, the first of these features was found to the northeast of Alpha Regio, on Venus.  It was one of the largest of these domes and therefore stood out. The strange feature was originally dubbed by the Magellan Project Science Team The Tick, because the many radiating ridges resembled the legs of a tick. Its concavity was likely confused as domelike as a tick's body, instead of the actuality which is that it is a bowl-shaped depression.  Through the first year of Magellan image data The Tick was thought to be a unique feature until an aide to the science team catalogued inconspicuous similar features all over Venus. This resulted in referring to the features as 'ticks' which was later changed to 'scalloped margin domes'.
caption: The original scalloped margin dome: The Tick
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