Q. Discuss the non-cyclic view of landscape development with special focus on the ideas of J.T. Hack.
The non-cyclic view holds that a landform assemblage is not a stage in a sequence from youth to old age, but the standing expression of a balance between the erosive energy of present processes and the resistance of the rocks they attack. Time is demoted from a cause to a parameter. J.T. Hack’s dynamic equilibrium model of 1960 is its fullest statement and the pivot on which post-Davisian geomorphology turned.
The Non-Cyclic Tradition Before Hack
- G.K. Gilbert (1877), in his Report on the Geology of the Henry Mountains, treated denudation as a mechanical balance two decades before Davis wrote the cycle.
- Law of equal action and law of divides — each element of a slope adjusts until it removes exactly what is supplied to it, and gradient steepens as catchment area shrinks towards a divide: statements of form with no reference to age.
- The graded stream — Gilbert’s river tends to a slope at which it just transports its load, restated by J.H. Mackin (1948) as the graded river and made measurable by Leopold and Maddock (1953).
- Davis’s Geographical Cycle (1899) eclipsed this strand until A.N. Strahler (1950, 1952) revived it as a statistical, open-system geomorphology on which Hack built.
Hack (1960): The Landscape as an Open System
Hack’s paper, “Interpretation of erosional topography in humid temperate regions” (American Journal of Science, 258-A), explained landscape from the processes operating in it now, and demonstrated lithological adjustment of form.
- Open system — energy and matter cross the boundary continuously, against Davis’s implicitly closed system running down to maximum entropy in a peneplain.
- Dynamic equilibrium — “the landscape and the processes that form it are part of an open system in a steady state of balance”. Every slope and channel is mutually adjusted.
- Uniform downwasting — erosion proceeds at the same rate in every part of the landscape, so each major outcrop yields an equal sediment load per unit area.
- Relief reflects resistance, not stage — hard rocks stand high, rugged and steep; weak rocks lie low and gently rolling. Form is explained by geological pattern.
- Time-independence — while the controls and the energy supply hold constant there is no appreciable change in landforms through time; the form persists as long as the controls persist.
- Ridge-and-ravine topography — Hack’s name for the normal equilibrium expression of a humid temperate landscape.
The Shenandoah Evidence
- Hack’s ground was the Shenandoah Valley and folded Appalachians (USGS Professional Paper 484, 1965), with J.C. Goodlett supplying the ridge-and-ravine study of 1960. Massanutten Mountain rides on resistant sandstone while the lowland beside it is floored on carbonates — relief mapping resistance, not elapsed time.
- Where resistance and drainage density are uniform and slopes stand at the same maximum angle, summits all reach roughly the same height, so the accordance mimics a dissected peneplain without ever having been one — making the Schooley, Harrisburg and Somerville “peneplains” an admissible artefact of lithology and stream spacing.
The Machinery That Followed
- R.J. Chorley (1962), “Geomorphology and General Systems Theory”, recast Davis as a closed system trending to maximum entropy and Hack’s as an open system in steady state, giving the non-cyclic view its systems vocabulary.
- Schumm and Lichty (1965), “Time, space and causality in geomorphology”, dissolved the quarrel by scale: in cyclic time (millions of years) time and initial relief are independent variables and Davisian reasoning holds; in graded time (100–1,000 years) they cease to matter and steady state holds; in steady time form is static.
- Schumm (1973, 1979) added geomorphic thresholds and complex response: effective erosion is episodic. His dynamic metastable equilibrium has form oscillating about a trending mean, punctuated by step-like jumps as a threshold is crossed, so terraces can arise internally with no external trigger.
Davis and Hack Compared
| Basis | Davisian cycle (1899) | Hack’s dynamic equilibrium (1960) |
|---|---|---|
| Reference system | Closed; runs down to maximum entropy | Open; continuous throughput of energy |
| Status of time | Independent variable; stage is the explanation | A parameter only; form is time-independent |
| Cause of relief contrast | Position in the youth–maturity–old age sequence | Rock resistance and process intensity |
| End form | Peneplain with monadnocks | None; ridge-and-ravine topography endures |
| Accordant summits | Uplifted, dissected peneplains | Uniform lithology and drainage density |
Applying the Model
- Aravalli quartzite ridges — resistant quartzite bands stand as narrow ridges above a gneiss and schist plain: lithological adjustment written across Peninsular India.
- Western Ghats — the crest is held by resistant basalt and charnockite while the Konkan lowland is cut in weathered rock, a contrast outlasting the Cenozoic.
- Chota Nagpur and Bundelkhand — accordant granite-gneiss surfaces read as uplifted peneplains admit an equilibrium reading too, which is why Peninsular erosion-surface counts stay contested.
- Himalaya — uplift is fast and unsteady, relief is tectonically driven and forms are unadjusted; the premise of constant controls fails outright.
Criticism and Modern Standing
- Equilibrium is asserted more often than demonstrated — steady state cannot be observed over human timescales, and a perfect fit between present processes and existing forms is a deduction without ground support.
- Relict and inherited forms are real — “to an extent all landforms are prisoners of their own evolutionary history” (R.J. Rice, 1977). Lateritic duricrusts and Deccan trap step-topography are inherited, and glacial, volcanic and tectonically active terrains never reach adjustment at all — Hack himself conceded that “the inheritance of form is always a possibility”.
- It explains form better than history — it says why a landscape looks as it does but predicts no sequence, which is why denudation chronology survives beside it; A.L. Bloom (1978) read it as an interpretive frame, not a law.
- Cosmogenic tests cut both ways — basin-wide ¹⁰Be in the Great Smoky Mountains gives erosion of about 27 metres per million years, uniform over 10⁴–10⁵ years (Matmon and others, 2003); in active ranges the same method finds order-of-magnitude variation, making steady state a special case.
Conclusion
Hack’s achievement was to make lithology and process, not stage, the explanation of form, and to give geomorphology a reference system that could be measured rather than narrated. But equilibrium is a condition, not a history. It accounts admirably for the adjusted ridge-and-ravine terrain of the stable Appalachians or the Aravalli ridges, and poorly for the Himalaya, where uplift outruns adjustment. Davis and Hack are scale-specific truths, not rivals.