The concept of thresholds in geomorphology

Exploring the changing processes of land forms is considered to be one of the key topics in geomorphological studies. Nowadays, geomorphological studies analyzes and clarifies geomorphic forms and processes at ground level. This shows the dominance of a systematic view in this field. In systematic view, geomorphic analyses are performed based on the relation between land form and process. Geomorphologic threshold is one of the key concepts in systematic theory and thus is of significant importance in geomorphology. It indicates borderline situations during the occurrence of changes and shows temporal changes. The present article is based on secondary research and exploits theoretical and applied concepts related to thresholds, seeking to reach a balanced systematic analysis. It tries to study geomorphologic thresholds and classifications using different Persian and English resources. Moreover, we propose a short overview of some geomorphological issues, such as gully erosion, alluvial fan and river systems. Results indicate that geomorphic thresholds separates different situations of a system and are thus distinguishable. In fact, occurrence of a threshold changes the dominant processes in a geomorphologic system. This concept shows the situation in which a process operates to establish a new balance in the system. Siyum classifies geomorphic thresholds into two categories: 1) Internal which is related to the inside of a geomorphic system and 2)external which is under the influence of external variables such as climatic and tectonic changes.