Strahler, Arthur (1918–2002)

Influential Pioneering Papers

Strahler produced a profoundly important series of papers. Initially, he introduced extremely simple statistical measures such as tests of significance, but sophisticated concepts such as dimensionless numbers (e.g., stream order, relief ratio, and the hypsometric curve) quickly followed. Dimensionless numbers were a critical contribution that permitted comparisons across many scales and produced insights previously masked by the shadow cast by scale differences. Perhaps the single most famous concept, among many, is the “Strahler order number.”

Within the Strahler stream-ordering system, a stream without tributaries is designated a first-order stream; on meeting another first-order stream, the united streams form a single second-order stream. Beyond this, any stream can absorb those of inferior order, but when meeting a peer, the two unite to become a single stream of the next higher order. In turn, this concept may be applied to drainage basins and associated fluvial concepts. This idea is one of the few to escape geomorphology to become essentially universal throughout science. Appreciation of the role of statistical randomness eventually constrained such research. In short, Strahler introduced a set of “timeless” concepts that did much to redress the then prevailing historical, or time-bound, perspective of geomorphology inherited from Davis.

The Systems Concept

Strahler also made important contributions to the introduction of systems concepts into geomorphology. In particular, he placed a very heavy emphasis on appropriate dimensional analysis in the equations used in a systems approach such that they are always appropriately balanced dimensionally. He also advocated the use of symbols derived from basic electrical circuitry as the most appropriate icons for creating diagrams of system models.

The Earth Science Educator

Strahler spent much of his later career as an independent author, producing innumerable introductory texts in physical geography, geoscience, and environmental science. Within his last publications is a significant attempt to counter the modern challenge to the science of creationism, later renamed creationist science.