The ob river can be found in:

north america
europe
africa
south america
asia

It can be found in "ASIA"

Hope this helps!

I'm pretty sure it's c. extremely gradual but not 100% sure though.

Magma forms by partial melting of upper mantle and crust. partial melt means that only a fraction of the available material forms a melt, and that the remainder stays solid. the partial melt rises because of its lower density and ascends through he crust. this is so conclusive mean the answer would be magma igneous rocks or balistic magma.