Here's why:

* Mafic magma is rich in magnesium and iron, and relatively poor in silica. This results in darker, denser, and more fluid lava flows.

* Felsic magma is rich in silica, and has a higher content of sodium, potassium, and aluminum. This results in lighter-colored, thicker, and more viscous lava flows.

Mauna Loa, like other Hawaiian volcanoes, is a shield volcano. Shield volcanoes are known for their gentle slopes and effusive eruptions that produce large volumes of fluid lava. These characteristics are consistent with mafic magma.