Why do river networks form different drainage patterns?
A drainage pattern is the map arrangement of a river and its tributaries. Branching reflects slope, rock resistance, fractures and landscape history, and can provide clues to underlying structures.
Main network forms
Tree-like dendritic networks can develop where rock resistance is relatively uniform. Parallel ridges and valleys encourage trellis patterns with tributaries joining main channels at roughly right angles. Channels following fractures or faults may show conspicuous rectangular turns. Streams flowing outward from a central high point, such as a volcanic cone, produce radial patterns. Natural networks can grade between patterns, and one basin may contain several.
Reading the map carefully
Interpret the whole basin and its mapping scale rather than a few short streams. Artificial channels, dams and urban development can alter natural drainage. A radial network does not prove that the landform is an active volcano; other central uplands can produce a similar pattern. Reliable interpretation combines topographic maps with geology and field observations, explaining why water follows particular routes rather than merely naming shapes.