River deltas such as the mississippi river delta developed due to
a. tectonic activity
b. the weathering of surface material
c. deposition of sediment by water, wind or ice

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.

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