Mass movements, erosion, and deposition

Q: What is the importance of a rotational slip plane in slumping?

It moves material downward in backward-tilted blocks In slumping blocks move downward along a curved slip plane. Exam tip: distinguish it from ordinary landslide by rotation.

Q: Which is the most reliable field indicator of soil creep?

Tilted trees and bent fences on a slope Soil creep is very slow movement so small tilts are its indicators. Exam tip: remember evidence that identifies slow movement.

Q: Why is solifluction more effective in periglacial regions?

The thawed upper soil flows over the frozen lower layer The frozen lower layer blocks drainage and thawed soil starts flowing. Exam tip: connect periglacial conditions with frozen ground.

Q: How can human road cutting increase instability in landslides?

It removes support from the slope base Cutting the slope foot can destabilize material above. Exam tip: include toe cutting among landslide causes.

Q: When is hydraulic action most effective in river erosion?

When fast flow increases air and water pressure in cracks Hydraulic action widens cracks by pressure and can break rock. Exam tip: remember fast flow and cracks together.

Q: What is the role of rock fragments carried by a river in abrasion?

They act as tools and scrape the bed and banks The direct answer is option A, they act as tools and scrape the bed and banks. Abrasion, also called corrasion, is erosion caused when sediment carried by a river strikes, rubs, and scrapes the river bed and banks. The moving water supplies the force, while pebbles, sand, and rock fragments act like natural cutting or polishing tools. Repeated impacts can enlarge the channel, smooth its sides, and wear down exposed rock. Option A is correct because it states the exact role of the transported rock fragments. Option B is wrong: fragments may obstruct a channel temporarily or form deposits, but they do not permanently stop every river. Option C is wrong because river load is carried and deposited on land or underwater, not only in the atmosphere. Option D is unrelated and scientifically overgeneralised; rock fragments do not always make water alkaline, and water chemistry depends on the minerals present. Do not confuse abrasion with hydraulic action: hydraulic action is the force of water itself, while abrasion is the scraping action of transported material. Memory cue: in abrasion, the load becomes the tool.

Q: The rounding of pebbles rolling in a river is most associated with which process?

Attrition by mutual collision Mutual collision of sediments makes them smaller and rounder. Exam tip: connect attrition with particle rounding.

01What is the most decisive physical difference between rockfall and debris flow?

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Answer and explanation

Correct answer: A. Free fall dominates rockfall while mixed material flows in debris flow

Rockfall is the falling of broken rock fragments on steep slopes. In debris flow water mixed loose material moves rapidly downslope.

Practice questions

01What is the most decisive physical difference between rockfall and debris flow?शैलपात और मलबा प्रवाह में सबसे निर्णायक भौतिक अंतर क्या है?

02What is the importance of a rotational slip plane in slumping?अवपात में घूर्णी फिसलन तल का महत्व क्या है?

03Which is the most reliable field indicator of soil creep?मृदा सर्पण को पहचानने का सबसे विश्वसनीय क्षेत्रीय संकेत कौन सा है?

04Why is solifluction more effective in periglacial regions?परिहिमानी क्षेत्रों में सोलिफ्लक्शन अधिक प्रभावी क्यों होता है?

05How can human road cutting increase instability in landslides?भूस्खलन में मानवीय सड़क कटान किस प्रकार अस्थिरता बढ़ा सकता है?

06What is the difference between debris flow and mudflow based on material composition?मलबा प्रवाह और कीचड़ प्रवाह में पदार्थ की संरचना के आधार पर अंतर क्या है?

07Which analysis is correct regarding erosion and mass movement?अपरदन और जन संचलन के संबंध में सही विश्लेषण कौन सा है?

08When is hydraulic action most effective in river erosion?नदी अपरदन में जलप्रहार का प्रभाव सबसे अधिक कब होता है?

09What is the role of rock fragments carried by a river in abrasion?घर्षण अपरदन में नदी द्वारा ढोए गए शैलखंडों की भूमिका क्या होती है?

10The rounding of pebbles rolling in a river is most associated with which process?नदी में लुढ़कते कंकड़ों का गोल होना किस प्रक्रिया से सबसे अधिक जुड़ा है?

11In limestone areas river or groundwater erosion is most associated with which process?चूना पत्थर क्षेत्र में नदी या भूमिगत जल का अपरदन किस प्रक्रिया से अधिक जुड़ता है?

12Which geomorphic result is produced by vertical river erosion?नदी की ऊर्ध्वाधर कटाई किस भूआकृतिक परिणाम को जन्म देती है?

13How does lateral erosion affect a river valley?पार्श्व अपरदन का प्रभाव नदी घाटी पर किस रूप में दिखता है?

14When does river deposition mostly begin?नदी निक्षेपण अधिकतर कब शुरू होता है?

15Under which spatial condition does an alluvial fan generally form?जलोढ़ पंख सामान्यतः किस स्थानिक दशा में बनता है?

16What is the relation between floodplain fertility and deposition?बाढ़ मैदान की उर्वरता का निक्षेपण से क्या संबंध है?

17Which processes dominate respectively on the outer and inner banks of a meander?विसर्प के बाहरी किनारे और भीतरी किनारे पर क्रमशः कौन सी प्रक्रिया प्रमुख होती है?

18What is the main process of oxbow lake formation?अश्वनाल झील बनने की मुख्य प्रक्रिया क्या है?

19Which combined erosion process causes waterfall retreat?झरने के पीछे हटने में कौन सा संयुक्त अपरदन कार्य करता है?

20What does gully erosion indicate?गली अपरदन किस बात का संकेत देता है?

21Why is sheet erosion often difficult to identify initially?शीट अपरदन को अक्सर प्रारंभ में पहचानना कठिन क्यों होता है?

22What does deflation mean in wind erosion?पवन अपरदन में अपवहन का अर्थ क्या है?

23Which combination is most suitable for yardang formation?यार्डांग बनने के लिए कौन सा संयोजन सबसे उपयुक्त है?

24What is the wind transport method in which sand grains move by bouncing?बालू के कणों की उछलकर आगे बढ़ने वाली पवन परिवहन विधि क्या कहलाती है?

25What is the key feature of loess deposits?लोस निक्षेप की प्रमुख विशेषता क्या है?

Analytics choices

01What is the most decisive physical difference between rockfall and debris flow?

02What is the importance of a rotational slip plane in slumping?

03Which is the most reliable field indicator of soil creep?

04Why is solifluction more effective in periglacial regions?

05How can human road cutting increase instability in landslides?

06What is the difference between debris flow and mudflow based on material composition?

07Which analysis is correct regarding erosion and mass movement?

08When is hydraulic action most effective in river erosion?

09What is the role of rock fragments carried by a river in abrasion?

10The rounding of pebbles rolling in a river is most associated with which process?

11In limestone areas river or groundwater erosion is most associated with which process?

12Which geomorphic result is produced by vertical river erosion?

13How does lateral erosion affect a river valley?

14When does river deposition mostly begin?

15Under which spatial condition does an alluvial fan generally form?

16What is the relation between floodplain fertility and deposition?

17Which processes dominate respectively on the outer and inner banks of a meander?

18What is the main process of oxbow lake formation?

19Which combined erosion process causes waterfall retreat?

20What does gully erosion indicate?

21Why is sheet erosion often difficult to identify initially?

22What does deflation mean in wind erosion?

23Which combination is most suitable for yardang formation?

24What is the wind transport method in which sand grains move by bouncing?

25What is the key feature of loess deposits?