The correct answer is option 2: earthquakes. Tsunamis are large ocean waves that are caused by underwater earthquakes, specifically those that occur along tectonic plate boundaries. When two tectonic plates move past each other or collide, the friction and stress between them can cause an earthquake. This seismic activity can then generate a series of powerful waves that travel through the ocean, resulting in a tsunami. It is important to note that not all earthquakes produce tsunamis, and tsunamis can also be triggered by other factors such as landslides or volcanic eruptions. However, the primary and most common cause of tsunamis is indeed earthquakes.