Part 3: Landforms & Water

What internal processes (plate tectonics) are responsible for the landforms in your location? This should include current processes (if any) and past events.

The island archipelago of Tonga sits at the intersection of two major tectonic plates – the Indo-Australian plate and the Pacific Plate. Tonga is part of the Pacific “Ring of Fire” that encircles the entire ocean basin. That crust is pushed towards Australia and Asia, riding on a partially molten mantle. Where it meets the edge of the Indo-Australian Plate in the east, the now cooled oceanic crust sinks back into the mantle along a “subduction zone." (2) There is also the Kermadec Trench which is the southern section of a very active line of plate tectonic collision (3). These are responsible for many volcanoes that are along side these ridges. Aside from that, there are not many other internal processes very close to Tonga, but there are many that surround the region.

Is your location near any plate boundaries? How does this affect the geology and landforms in the area?

The islands that make up the kingdom of Tonga are located on the junction of two tectonic plates. To the east of the archipelago is the Pacific plate that is subducting beneath the Indo-Australian plate to the west. Tonga is on the "Ring of Fire" that encircles the Pacific Ocean. Because of Tonga's location on a subduction zone, many of the islands are formed by volcanoes and volcanic lava-flows. Other islands are formed from coral limestone that has been uplifted by tectonic plate activity (4).

What weathering and erosion processes affect the landforms in your area? This should include current processes (if any) and past events.

Many of the weathering and erosion processes that affect Tonga can be found along the coasts of the islands. For instance, Tonga experiences a lot of beach erosion which is the loss of beach sand due to a combination of wind and water movement. Sand is picked up off the beach and transferred to deeper water or another coastal spot on the island (5). This is a continual process that can be seen on the Tongan islands because it is surrounded by water. Because of this, the islands' shape and many of their landforms are constantly changing due to the weathering and erosion.

How have glaciers impacted the landforms in your location? (if at all)

Tonga does not have any glaciers since it is a tropical island, but it is still heavily impacted by glaciers from around the world. As the earth's northern and southern glaciers melt, the sea rises far more here than elsewhere in the world. This is especially important because much of the residents of tonga rely on agriculture and fishing methods so having this rise in sea level can be detrimental to their economic systems (7).

What other processes (not yet discussed) have shaped the landforms in your area? (wind, waves, etc?)

One of the interesting things about Tonga is that it is made up of many islands. With this being said, the weathering and erosion of sand and rocks from the seawater is working in its favor to help change and shape many of the landforms in the area. In fact, it is predicted that the interactions of the warm seawater and ash spewing from the volcano created a material called "tuff" that hardened along the shoreline. So unlike other ephemeral volcanic islands whose rocky and ashy shorelines slowly wash away, the tuff has given the new island some extra stability (8).