[Blog] Distant Tsunamis: A Real Threat to Mauritius

Although Mauritius has never been hit by a major tsunami, it has experienced scenarios serious enough to warrant concern. The complexity of natural phenomena, combined with the island's geographical position—affected even by distant tectonic plates—serves as a reminder that anything can change in an instant. This highlights the importance of being prepared for any eventuality.

Tsunamis and Climate Risks: A Dual Threat to Coastal Communities

Last week, a powerful underwater earthquake measuring 8.8 on the Richter scale, occurred off the Kamchatka Peninsula in Russia, triggering tsunami alerts across the Pacific Ocean. The tsunami waves reached the northern coasts of Japan, Alaska, Hawaii, and parts of California, leading to evacuations, emergency alerts, and heightened surveillance across multiple time zones.

While this particular tsunami originated from geophysical factors and is not directly linked to climate change, it starkly reminds us of Mauritius’s vulnerability and that of its coastal communities. With rising sea levels, existing saline intrusion, and the increasing frequency of extreme weather events like cyclones and coastal flooding, climate risks compound the already present natural hazards.

This event raises new challenges for Mauritius, underscoring the urgency to implement integrated risk management strategies that combine geophysical early warning systems with climate-resilient planning to protect lives and livelihoods in coastal areas worldwide.

Tectonic Plates: An Invisible Natural Nuisance

Tectonic plates are large, rigid plates that make up the Earth's crust and the upper part of the mantle (known as the lithosphere). These plates rest on a softer, slowly flowing layer of rock (the asthenosphere) beneath them and gradually move over time, resembling icebergs drifting on the ocean's surface.

There are seven major tectonic plates, including the Pacific, Eurasian, and African plates, along with many smaller plates that collectively form the Earth's outer shell. While tectonic plates themselves are not inherently dangerous, the movement along their boundaries causes geological instability within the Earth.

These interactions occur mainly in three ways:

1. Divergent boundaries: plates move apart from each other, often leading to seafloor expansion, minor earthquakes, and volcanic activity.
2. Convergent boundaries: plates move toward each other, resulting in mountain formation, volcanic eruptions, or subduction, where one plate is pushed under another.
3. Transform boundaries: where plates slide past each other, often associated with significant earthquakes due to the sudden release of accumulated stress along faults.

Essentially, the movement and interaction of tectonic plates continuously reshape the Earth's surface, creating powerful natural phenomena such as earthquakes, tsunamis, volcanoes, and mountain ranges.

The Dynamic Impact of the Earth’s Internal Structure

Understanding the Earth’s internal structure is vital, not only for geologists but for developing early warning systems, risk reduction strategies, and resilient communities facing natural hazards.

The Earth consists of four main layers: the crust, the mantle, the outer core, and the inner core. Each layer has distinct physical states and chemical compositions, playing essential roles in the formation and evolution of our planet.

The crust is the outermost layer, thin and solid, where we live.

Beneath it lies the mantle, a thick layer of semi-solid rock extending about 2,900 kilometers deep.

Below the mantle is the outer core, a liquid layer primarily made of molten iron and nickel, responsible for generating the Earth’s magnetic field.

At the center is the inner core, a solid sphere mainly composed of iron and nickel, kept solid by immense pressure despite extreme temperatures.

The Tectonic Mechanics Behind Tsunami Formation

Tsunamis are most often caused by convergent plate boundaries, particularly in subduction zones where one tectonic plate is forced under another. Here’s how it works:

When two plates converge, the oceanic plate usually sinks beneath a continental plate or another oceanic plate.

Over time, as the plates lock together, stress accumulates at the subduction zone.

When this stress is suddenly released, typically in the form of a megathrust earthquake, it can cause a sudden uplift or subsidence of the ocean floor. This abrupt vertical movement of the seabed displaces a massive amount of water, generating tsunami waves that quickly propagate across the ocean.

The Case of Mauritius and Tsunamis

Mauritius is located on the Somali plate and owes its volcanic origin to the Reunion hotspot. Unlike regions near tectonic plate boundaries, our island is situated within the plate, far from collision or subduction zones typically associated with significant seismic activity.

Several factors have contributed to deflecting and mitigating the impact of tsunami waves on the coastal regions of the southwestern Indian Ocean islands, including Mauritius. These include the mitigating influence of ocean currents along the Equator, combined with the topography of the Mascarene Plateau, where some parts plunge up to 147 meters below sea level.

These shallow underwater formations can alter the trajectory of tsunami waves and potentially reduce their energy before reaching the island’s shores.

Rodrigues is a Different Story

For Rodrigues Island, the situation is different. About 300 km east of the island is a highly geologically active area known as the "Rodrigues Triple Junction," as well as the "Mid-Indian Ocean Ridge" (MIOR). This tectonic junction, located at latitude 19 degrees South, is where three major tectonic plates—African, Antarctic, and Indian—meet. It is a region where geological processes are particularly active.

Moderate earthquakes (magnitude 5.0) frequently occur on the ocean floor east of Rodrigues. However, there is no evidence that these events have generated destructive tsunamis affecting the island.

The Role of the Sunken Continent Beneath Mauritius: A Geological Boon

The story begins in 2013, when a research team led by Professor Torsvik from the Centre for Earth Evolution and Dynamics (CEED) at the University of Oslo collected sand samples from a beach in Mauritius for geological analysis.

In some of these tiny grains of volcanic rock, researchers found microscopic zircon particles—minerals much older than the island itself. This unexpected discovery revealed that Mauritius’s geological history is far older than previously believed.

Laboratory analyses confirmed that the island's relatively young volcanic formations cover fragments of ancient continental crust, once attached to a supercontinent connecting India and Madagascar about 85 million years ago. Professor Torsvik proposed the name "Mauritia" to refer to this long-lost sunken continent.

In a more recent study, Professor Torsvik—together with Lewis D. Ashwal (University of the Witwatersrand, South Africa) and Michael Wiedenbeck (GFZ, responsible for SIMS analyses)—uncovered further evidence of this continent hidden beneath Mauritius, reinforcing the hypothesis of its existence.

Seismic Considerations Should Not Be Overlooked

However, some potential dangers remain. While Mauritius is not located on an active tectonic plate boundary, scientists believe that fragments of ancient continental crust, like "Mauritia," may retain residual tectonic characteristics (e.g., faults or fracture zones).

Although it is unlikely that these areas would cause major tsunamis, the accumulation of tectonic stress could theoretically trigger minor seismic activity or indirectly influence wave behavior, amplifying them in some cases.

However, some facts must not be overlooked, including:

• The proximity of Mauritius to the Rodrigues Triple Junction, located about 300 km east of Rodrigues. This tectonic junction, where the African, Indian, and Antarctic plates meet, is seismically active. Although earthquakes there are rare, they could trigger regional tsunamis.

The Risk of Tsunamis Across the Indian Ocean

Events like the 2004 Indian Ocean tsunami (caused by a magnitude 9.1 earthquake off Sumatra) show that mega-earthquakes far away can affect countries thousands of kilometers away. At that time, Mauritius recorded wave activity but suffered no significant damage.

The Impact of Climate Change

The fact is that even small tsunamis could pose increased risks in the future due to climate change, rising sea levels, and the increasing urbanization of coastal areas.

Mauritius is considered to have a low to moderate risk of tsunamis, as it is not situated on an active tectonic plate boundary, meaning it is far from major subduction zones (like those near Sumatra or the Pacific Ring of Fire), where most major tsunamis originate. However, it is not entirely safe.

The island benefits from some geological stability as it rests on the Somali plate, well inside it, making the occurrence of local earthquakes that generate tsunamis extremely unlikely.

It should also be noted that the Mascarene Plateau, along with any remnants of the sunken continent "Mauritia," forms ridges and shallow underwater areas that could deflect, disrupt, or mitigate the energy of tsunami waves before they reach the coast.

The primary concern lies with distant-origin tsunamis and regional seismic activity near tectonic junctions. In this context, preparedness, early warning systems, and public education remain essential.

The Interaction Between the Sunken Continent "Mauritia" and Tsunamis

The interaction between the sunken continent "Mauritia" and tsunamis is subtle but scientifically fascinating. Scientists believe it clearly acts as a natural barrier. Although "Mauritia" does not directly cause tsunamis, its geological structure and topography in the southwestern Indian Ocean could influence how tsunami waves propagate in the region.

Some parts of "Mauritia," now buried under volcanic rocks and marine sediments, could form underwater ridges, plateaus, or shallow areas capable of disrupting or deflecting tsunami waves' propagation. This could also diminish wave energy before it reaches the nearby shores of Mauritius, as well as other islands like Reunion or Seychelles.

This submerged continent may play a role similar to that of the Mascarene Plateau, known for its influence on ocean currents and wave dynamics. It is also scientifically proven that emerging continental crusts like "Mauritia" can cause wave refraction, redirecting their energy toward certain areas or away from others.

Ultimately, the role of "Mauritia" in tsunamis lies not in their generation but rather in the potential to modulate or mitigate their impact through its submerged geological structures and influence on the seafloor topography.