Final answer:
Valparaíso is closer to a major plate boundary than Helena. It is near the convergent boundary between the South American Plate and the Nazca Plate, leading to frequent earthquakes and volcanism in the region.
Step-by-step explanation:
The city that is closer to a major plate boundary is Valparaíso. On the west coast of South America, particularly in Chile, there are significant tectonic activities due to the boundary between the South American Plate and the Nazca Plate. Valparaíso is located near this convergent plate boundary, where the oceanic Nazca Plate is subducting beneath the continental South American Plate. This area is known for its high seismic activity and the presence of the Chilean Trench. The subduction zone leads to frequent earthquakes and a line of volcanoes stretching along the continent’s edge, part of the Pacific “Ring of Fire.”
In contrast, Helena, the capital city of Montana, USA, is located much farther from any tectonic plate boundaries. It is situated within the interior of the North American Plate, far from the active boundaries on the coast. The nearest plate boundary to Helena is the transform boundary represented by the San Andreas Fault in California, which is still hundreds of miles away to the southwest.