Chaotic Terrain (Venus)

Definition

Chaotically collapsed terrain occurring at the source region of Venusian outflow channels (Kargel et al. 1994).

Formation

Its origin is likely similar to chaotic terrain formation on Mars. Lava suddenly withdrew from a subsurface reservoir while the overlying rock collapsed, and rapid subsequent drainage eroded the channel (Baker et al. 1992; Ford et al. 1993; Komatsu 1993; Kargel et al. 1994).

Prominent Examples

The source region of Kallistos Vallis consists of graben-forming coalesced fractures that are flooded by lava and widened by slumping, collapse, and sapping. Its floor near the edges contains “a chaotic jumble of rocks,” 0.6–2 km across. The chaos area is few 10’s km in diameter (Kargel et al. 1994) (Fig. 1).

Fig. 1

Chaotic source of an outflow valley on Venus, on the southwest flank of Ammavaru volcano (Ford et al. 1993). Scale bar 10 km. Magellan left-looking radar mosaic (NASA/JPL/USGS) (Cf. Fig. 14 from Baker et al. (1992), Fig. 7b from Kargel et al. (1994))