问一逻辑题的语法结构

lr_winter

Charcoal from a hearth site in Colorado, 2,000 miles south of Alaska, is known to be 11,200 years old.  Researchers reasoned that, since glaciers prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago, humans must have come to the Americas more than 18,000 years ago.

gwd的一道cr，我不确定阴影部分的结构，推测意识是“阻止人类从Alaska-Siberia”大陆桥向南迁移，migration和south和from是什么修饰关系？这是什么语法点呢？

AlienX

idiom: prevent someone from (doing) something.
south是副詞, 照道理不能修名詞...可是我覺得它是修migration這個名詞...可能個為migration這個字含有動作, 所以可以用south去修...not 100% sure...