Ina has been onboard the research vessel gustavo, off the coast of chile, for several weeks now. she is measuring the depth of a very deep trench in the ocean that runs parallel to the coastline. in the distance, she notes a great mountain range on the mainland. suddenly, she is notified that a submarine earthquake just occurred below the trench, generating a tsunami. as marina puts on her lifejacket, she recalls the type of plate boundary nearby that led to the trench formation.

The correct answer is - convergent plate boundary.

The western coast of South America is a home to a convergent plate boundary, between the Nazca oceanic tectonic plate and the South American continental tectonic plate.

The Nazca plate is lower and heavier, thus it subducts bellow the higher and lighter South American plate. This subduction is causing a lot of geologic activity in the region, with the Andes Mountain Range being one of the products, as well as the common earthquakes, and the volcanic activity.

Since there's often earthquakes that appear under water, the chances of a tsunami are always high, especially if it is a stronger earthquake, which is why the people living in this part of the continent are always on alert.