(a)(i) Formation of erosional plains.
They are formed by agents of denudations such as rivers, wind, rain and ice. Irregular surface are often smoothened out to form plains. Different types of plain results from agents of denudation and refers to as pereplains while those fashioned by wind as agent of denudation are called pediplains. In arid regions and semi arid regions, wind deflation lowers level of land to form extensive plains whereas in glaciated regions, glaciers and ice sheets. scour and level the land to form ice — scoured plains.
(ii) Formation of Dissected plateaux.
This is a product of weathering and denudation. It is the wearing down of extensive plateau by wind, water, rain and ice. This action creates narrow deep valleys in the plateau described as dissected plateau. Very good examples are: The Scottish highlands, the Jos Plateau etc. In dry areas, corrosion by rivers and abrasion by wind dissect the plateau resulting into mesas and buttes.
(b) Advantages of plains;
(i) Rich sources of minerals
(ii) provide fertile agricultural lands
(iii) centres of population concentration
(iv) plains are good for settlement
(v) favour communication lines - roads and railways
(vi) favour growth of pasture and so encourage animal rearing
(vii) concentration of industries
(viii) flood plains of rivers favour development of ports.
Disadvantages of plains
(a) Not a good defence centre
(b) May be waterlogged
(c) Liable to flooding especially delta areas
(d) May be barren e.g outwash plains in some parts of The Netherlands.
(e) May present problem to communication especially when flooded .