Sudden, Dramatic Change in Soil Layers

[sea.thunter7]

Based on experience digging deep holes in the Philippines, how many of you have had the soil layer suddenly change from a sand/gravel mixture to pure topsoil? Soil just like what is found at the 1-4 ft layer. Geologically speaking, why would topsoil occur naturally at a depth of 30 ft? It seems like any topsoil left behind at this depth would have occurred millions of years ago. Over that time, wouldn't it have mixed in with the sand and gravel?

 

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[Kray Gelder]

Are you still talking about the Philippines, where this soil layer is? If located in a mega-thrust earthquake area, what you describe could happen over hundreds, not millions of years.

 

[bologna321]

Flood, landslide, human intervention...

 

[smokeythecat]

And Tsunamis.

 

[sea.thunter7]

Are you still talking about the Philippines, where this soil layer is? If located in a mega-thrust earthquake area, what you describe could happen over hundreds, not millions of years.

Flood, landslide, human intervention...

And Tsunamis.

Thanks for the replies.