I realise now from your previous question that the phenomenon in question is "El Nino". I did a quick search for Peru, ancient civilizations, El Nino, and found some interesting information on ancient people called the Moche. I don't know how this became الموسن in your text, but you never know...

Here is what I found:

But then Steve Bourget found evidence of enormous rain damage at a Moche site called Huancaco which he could date. Here new building work had been interrupted and torn apart by torrential rain, and artefacts found in the damaged area dated to almost exactly the period Thompson had predicted there would have been a mega El Nino. Thompson's theory seemed to be stacking up.

Then archaeologists began to find evidence of Thompson's mega drought. They found huge sand dunes which appeared to have drifted in and engulfed a number of Moche settlements around 600 to 650 AD. The story all fitted together. The evidence suggested the Moche had been hit by a doubly whammy: a huge climate disaster had simply wiped them out.

For several years this became the accepted version of events; the riddle of the Moche had been solved.

http://www.tv.com/the-lost-civilisation-of-peru/episode/4168...

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Note added at 1 hr (2006-03-16 22:37:09 GMT)
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From an article called "The Lost Civilisation of Peru".