The correct option is 1 and 3 only.
Explanation
Fluvial depositional landforms are created when the velocity of running water decreases, reducing its capacity to transport sediment. Two prominent landforms resulting from this process are alluvial fans (formed at foothills where gradients change abruptly) and deltas (formed at the river mouth where the river enters a standing body of water).
Statement 1 is Correct:
Alluvial fans are formed when streams flowing from mountains break into foot slope plains of low gradient. The load is dumped as a broad cone. In humid areas, alluvial fans normally appear as low cones with gentle slopes from head to toe. In contrast, in arid and semi-arid regions, they often form high cones with steep slopes due to ephemeral and flashy water flow.
Statement 2 is Incorrect:
In deltas, the deposition process is governed by the reduction in stream velocity as it enters a sea or lake. The coarser and heavier materials settle out first near the river mouth. The finer fractions, such as silts and clays, are carried further out into the sea and settle later. Therefore, the finest materials do not settle first.
Statement 3 is Correct:
The sorting of sediments differs significantly between these two landforms. Alluvial fans are typically composed of poorly sorted load because the stream dumps its sediment quickly as the flow spreads out. Conversely, delta deposits are formed in standing water, allowing sediments to settle according to size and weight. As a result, delta deposits are very well sorted with clear stratification.
Key Takeaway:
Alluvial fans are poorly sorted, cone-shaped deposits found at foothills, whereas deltas are well-sorted, stratified deposits found at river mouths where coarse material settles near the shore and fine material settles further offshore.