3.1 BASIC CONCEPTS OF GEOMORPHOLOGY AS POSTULATED BY THORNBURY PRANABPATI KARMAKAR ASSISTANT PROFESSOR DEPARTMENT OF GEOGRAPHY BANGABASI COLLEGE

William D. Thornbury 1900-1986 ● Thornbury was bom in English, Indiana, on April 23, 1900, the son of Frank and Belle Thornbury. After attending primary and secondary schools in English, he enrolled at Central Normal College in 1918 in Danville,Indiana,in order to become a high school teacher. After one year of college, he taught history, Latin, and algebra at Alton High School in southern Indiana; the following year, 1920 William David Thornbury, a Fellow of the Geological Society of America and best known for his outstanding book Principles of Geomorphology, passed away at his home in Bloomington, Indiana, on November 12, 1986, after an extended period of failing health.

Pliestocene ice age, 10000 yrs ago uniformitarianism 1. The same physical processes and laws that operate today operated throughout geologic time, although not necessarily with the same intensity as now (Hutton's principle of uniformitarianism) 1785- Hutton-”The present is the key to the past” Holocene (Recent) Pliestocene ice age, 10000 yrs ago

PRESENT IS THE KEY TO THE PAST

uniformitarianism

Control of Geologic structure on landform 2. Geologic structure is a dominant control factor in the evolution of land forms and is reflected in them Control of Geologic structure on landform GEOLOGICAL STRUCTURES ARE------ FOLDED STRUCTURE FAULTED STRUCTURE HORIZONTAL STRUCTURE VERTICAL STRUCTURE DOMAL STRUCTURE

FOLDED STRUCTURE

HORIZONTAL STRUCTURE

FAULTED STRUCTURE

UNICLINAL STRUCTURE

DOMAL STRUCTURE

VERTICAL STRUCTURE

MORE EROSION = LOW ALTITUDE LAND 3. To a large degree the earth's surface possesses relief because the geomorphic processes operate at differential rates Relief as a result of differential erosion POTENTIAL ENERGY= m X g X h(where m= mass, g= gravity and h= height) MORE EROSION = LOW ALTITUDE LAND LESS EROSION = HIGH ALTITUDE LAND

Each geomorphic process develops distinctive landform 4. Geomorphic processes leave their distinctive imprint upon land forms and each geomorphic process develops its own characteristic assemblage of land forms Each geomorphic process develops distinctive landform Endogenetic Processes: Vulcanic eruption, Tectonic movement, Earthqueak, Tsunami Exogenetic Processes: Fluvial Process Glacial Process Aeolian Process Coastal Process etc.

5. As the differential erosional agents act upon the earth's surface there is produced an orderly sequence of land forms An orderly sequence of landforms by the act of geomorphic agent YOUTH MATURE OLD

6. Complexity of geomorphic evolution is more common than simplicity Most of the landforms possess complex evolutionary history On the basis of origin of history landforms are divider into five groups: 1. Simple Landforms: one energy and one erosional cycle 2. Compound Landforms: more than one energy 3. Mono-cyclic Landforms: one erosional cycle 4. Multi-cyclic Landforms: more than one erosional cycle, e.g- dissected plateau, Accordant summit level, Multi planation surface 5. Exhumed or Resurrected Landforms: due to denudational process, multi erosional cycle.

Age of the earth Topography 7. Little of the earth's topography is older than Tertiary and most of it is no older than Pleistocene Age of the earth Topography 90% landforms are Tertiary and before Pleistocene era e.g.- Mountain, river, valley, lake etc

●Idea of geologic and climatic changes during Pleisticene is important 8. Proper interpretation of present-day landscapes is impossible without a full appreciation of the manifold influences of the geologic and climatic changes during the Pleistocene ●Idea of geologic and climatic changes during Pleisticene is important Glaciated cover area 10,000,000 sq km. in Asia, Africa mainly North Pole Two aspect are very important Geology Climate

Geology and Climate

Geology and Climate

9. An appreciation of world climates is necessary to a proper understanding of the varying importance of the different geomorphic processes Differentcein climate is responsible for difference in geomorphic processes: Climate: Tropical(hot), Temparate(moderate), Polar(cold) Geomorphic processs : Fluvial, Aeolian, Costal, Glacial etc.

Climate and Geomorphological Processes

Climate and Geomorphological Processes

10. Geomorphology, although concerned primarily with present day landscapes attains its maximum usefulness by historic extension Present day Landscape attains historical extension (Fossils, Human Skeleton, Dendrochronology etc)

Historical extension

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