What role did white northerner play in the boycott?

By bringing publicity to the activism.

Explanation:

In 1955, a woman named Rosa Parks decided to sit in the bus seat that's preserved only to white citizens, which led to her arrest.

This action might sounds like nothing today. But in the past, many states in America imposed a racial segregation that prohibit black citizens to use the infrastructures that's exclusively given to the white people.

in respond to this arrest, many progressive activists in northern starts started to conduct a protest and call for a boycott to the Montgomery Bus that became the center of the incident. This increase the national support to abolish racial segregation that eventually led to the creation of the Civil Rights Act in 1964.

b toward the volcano.landward. the landward side of something is the side nearest to the land or facing the land, rather than the sea.

b: to eliminate competition from other farmers