During the Holocene between ∼300 and 1100 Mt/y were delivered by the Indus River to its lower alluvial plain and delta (Clift and Giosan, 2013). Immediately before the 20th century damming activities started, the Indus deposited ∼60% of its total load along its lower alluvial plain: with more than 600 Mt/y entering the alluvial plain and
only 250 Mt/y reached the delta (Milliman et al., 1984). This relationship holds at the scale of the entire Holocene with roughly half of sediment discharge by the river contributing to the aggradation of the lower alluvial SCH727965 plain and subaerial delta and the other half contributing to the progradation of both the subaerial and subaqueous delta (Clift and Giosan, 2013). Schumm et al. (2002) consider the modern Indus plain to be comprised of two inland alluvial fans, one focused north of Sukkur and the other near Sehwan, with avulsions occurring near the apex of these fans. Based on higher resolution data, we see the floodplain more as a series of prograding and overlapping sediment fans or deposits (Fig. 2 and Fig. 3) that reflect the movement of the historical
Indus River (cf. Fig. 1). Schumm et al. (2002) regard the avulsions to be controlled by tectonics GS1101 because avulsions appeared to have occurred repeatedly at the same location. The area containing Jacobobad-Khaipur lies close to the frontal folds of the Sulaiman lobe (Szeliga et al., 2012) and hence is influenced by incipient local fold-and thrust tectonics. The area immediately east of Karachi lies near an east-verging fold and thrust belt (Schelling, 1999 and Kovach et al., 2010), whereas the eastern delta including the Rann of Kachchh is subject to footwall subsidence associated with reverse faulting of the Kachchh mainland and other faults (Jorgensen
et al., 1993, Bendick et al., 2001 and Biswas, 2005). That natural avulsions were ADAMTS5 triggered by tectonic events is further evidenced by the fact that Mansurah (25.88° N, 68.78° E), the Arabic capital of the Sindh province, was destroyed by an earthquake c. 980 AD (Intensity ≈VIII), resulting in a post-seismic avulsion of the river (Fig. 3 inset, Bilham and Lodi, 2010). Since natural levees have been observed in India to collapse during intensity VII shaking, it is unnecessary to invoke co-seismic uplift as a requirement for upstream river avulsion (Bilham and Lodi, 2010). A similar possibly modest earthquake that occurred in 1668 in the historical province of Nasirpur destroyed the town of Samawani (Fig. 3) and again initiated avulsion of the Indus main channel (Bilham and Lodi, 2010). Levee breaching during significant flood events is thought to be directly responsible for other historical river avulsions (Holmes, 1968).