THE VOLCANOES OF THE LACHESIS TESSERA QUADRANGLE (V-18), VENUS

The Lachesis Tessera quadrangle (V-18) is located from 25o-50oN and 300o-330oE on Venus. Exposures of various volcanic materials superpose regional plains throughout the quadrangle, including the materials of four central volcanoes, flows from numerous shield fields, and assorted isolated flows. The shield field flows are areally significant flow fields associated with abundant small shields, most of which are about 10 km in diameter. Most exposures are moderately brighter in radar imagery than the regional plains, but in one locality the shield flows are darker than regional plains. Small shields similar to those within the shield fields are common as isolated small groups or individuals superposed on the older of the two regional plains units identified within the quadrangle. Isolated flows are mostly moderately bright, relatively rare, digitate flows that generally do not have a resolvable construct at their source.

Only one named volcano, Eostre Mons, is located within the quadrangle, at 45.1°N, 329.1°E. Eostre Mons is 26 km in diameter with ~250 m of relief. It has small field of moderately bright flows surrounding it and is located adjacent to a shield field.

Central volcano A has ~850 m of relief and a large field of digitate flows extending east and northeast from a source caldera at 28.5oN, 326.3oE. The caldera is characterized by multiple, very bright, concentric rings; it is about 50 km in diameter. Flows have variable brightness but are mostly moderately bright. Proximal flows are smaller and probably younger than distal flows.

Central volcano B (located at 36oN, 317.5oE) is surrounded by a field of digitate flows of variable brightness, with the brightest (roughest) parts of individual flows located farthest from the source caldera. Flows extend generally eastward. There is no topography data coverage of the volcano.

The caldera of central volcano C (located at 38.2oN, 322.6oE) is primarily identified in topography data, as it is partly in a radar imagery data gore. The caldera is 112 km in diameter and the volcano has at least 1 km of relief. A large field of dark digitate flows extend away from the caldera in all directions, partially covered by younger, brighter flows. Proximal to the caldera radial graben deform the flows, but further away the flows are deformed by several sets of lineaments and a fracture belt.