There are many theories behind the sudden decline of Harappan civilization. Most common ones are discussed below:
- Destruction by floods-
It is believed that repeated floods caused Mohenjodaro people to desert the area and decline of civilization. I some area thick silt deposits of 80n feet have been found.
Raikes’s hypothesis says that the flooding which raised the ground by 30 feet is not normal; instead here we have evidence of 80 feet. It says that due to earthquake, tectonic upliftment took place on the mouth of river Indus. This led to impounding of water behind the raised part of the river. It suddenly poured the water in surrounding areas which got converted into lake. Civilisation could not survive this and declined.
Criticism- HT lambrick says that it is not possible due to 2 reasons-
- Earthquake raised bund must have breached by the water of Indus as happened in Sind in 1819 where earthquake raised bund was breached by the smaller streams of Indus called Nara.
- Silt will be deposited at the bottom of the river , not at Mohenjodaro where it will only parallel the surface.
Thus theory fails to tell about the decline of settlements in areas outside of Indus system.
- Diversion of Indus
Lambrick gave his own theory according to which the silt deposited because of wind action, not because of floods. He said, Indus has unstable floor so it shifted many times in its course. It led to lack of water and ultimately desertion of the Mohenjodaro and surrounding areas.
Criticism- if people knew about the shifting river bed why could not they shift to another area and establish second Mohenjodaro.
- Aridity and drying up of the river
This theory has been given by D.P.Aggarwal and Sood. They proposed that around 1500 B.C. aridity increased in the areas Harappan civilisation was situated in. further river Ghaggar Hakra dried up due to tectonic disturbances which changed the river regime. This led to harsh conditions and ultimately decline of agriculture, therefore of civilsation.
Criticism- arid conditions at that time has not been properly evidenced and driying up date of Ghagara is unknown.
- Invasion by Aryans-
Wheeler gave this theory which says that Aryan invaders who were very barbaric destroyed or completely routed native population.
Evidences- rig veda mention Dasa and Dasyus. Vedic god purandra is also mentioned which means destroyer of forts.
Criticism- Aryans arrived not early than 1500 B.C. but Harappa declined around 1800 B.C. so there is no firm evidence of clash between Aryans and Harappans
5. Recent discovery said that this civilsation declined beacause of radiation effects. this theory is not properly dated and have not been understood fully.
so as of now there is no proper theory to confirm the decline of Harappan civilsation. studies are going on and have taken pace from last 2 years in India. But unfortunately same level of enthusiasm is not shown by Pakistan and Afghanisthan governments due to terrorism and extremism in those areas.