Massive Greenland Landslide: Triggering Nine-Day Seismic Waves Worldwide
Massive Greenland Landslide: Triggering Nine-Day Seismic Waves Worldwide
Sub :Geo
Sec: Geomorphology
Why in News
On September 16, 2023, seismic stations worldwide detected an unusual signal that puzzled scientists. Unlike typical earthquakes, this event was caused by a massive landslide in Greenland’s Dickson Fjord. The landslide displaced water, triggering a mega-tsunami and sending seismic waves reverberating across the globe for nine days. The incident highlights the increasing risks posed by melting glaciers in a warming climate.
The Landslide Event
Location: Dickson Fjord is situated in eastern Greenland, part of the vast fjord systems of the Arctic region.
Depth and Width: The fjord has an approximate depth of 540 meters and a width of 2.7 kilometers, which makes it capable of containing large volumes of water and rock displaced by landslides.
Mega-Tsunami Site: In September 2023, Dickson Fjord was the site of a massive landslide that triggered a 200-meter-high mega-tsunami, which displaced approximately 25 million cubic meters of ice and rock.
About Fjords: A fjord is a long, narrow, deep inlet of the sea between high cliffs or steep slopes, typically formed by the process of glacial erosion.
Geographical Distribution: Fjords are most commonly found in high-latitude regions, especially in areas with a history of glaciation.
Major Fjord Regions:
Norway: Known for having some of the longest fjords in the world.
Greenland: Contains some of the largest fjords, such as Dickson Fjord.
New Zealand: Famous fjords like Milford Sound.
Canada: Fjords are found along the coast of British Columbia and eastern Quebec.
Formation of Fjords: Fjords are formed by the process of glacial erosion. Over time, glaciers carve deep valleys into the Earth’s crust, which later get filled with seawater when the glaciers retreat.
There are two main ways fjords are formed:
A. Glacial Carving: As glaciers move slowly over the land, they erode the underlying bedrock. The glacier carves a U-shaped valley, which is characteristic of fjords. When the glacier retreats, the sea floods the valley, creating a fjord.
Key Feature: Fjords often have steep sides or cliffs and a flat valley bottom.
B. Tectonic and Glacial Interaction: In some cases, tectonic activity (such as the movement of Earth’s crust) causes the land to uplift, while glaciers further shape the landscape by carving valleys. This process results in deeper fjords and sometimes more complex fjord systems.
Example: Fjords in Norway and Greenland, where tectonic uplift contributed to their depth and steep slopes.
Key Features of Fjords:
Deep Inlets: Fjords can be extremely deep. For example, Sognefjord in Norway is over 1,300 meters deep.
Steep Cliffs: Fjords are typically surrounded by high, steep cliffs that can rise dramatically from the water.
U-Shaped Valleys: The valleys formed by fjords are U-shaped due to the glacier’s erosive action.
Long, Narrow Inlets: Fjords are long and narrow, with their length often extending deep inland.
Characteristics of Fjords:
Sill: Many fjords have a shallow area called a sill at their mouth, where the glacier’s terminal moraine (a pile of debris left by the glacier) restricts the water flow.
Seiche: Fjords can experience a phenomenon known as seiche, where waves reflect back and forth within the inlet, as seen in the Dickson Fjord after the 2023 landslide.
Cold-water Coral Reefs: Some fjords, such as those in Norway, are home to unique cold-water coral reefs.
About Sloshing Waves (Seiche Effect): The mega-tsunami waves reflected back and forth within the 540-meter-deep, 2.7-kilometer-wide fjord. These oscillating waves created a “seiche” that persisted for over nine days, with a maximum wave amplitude of 7.4 meters and an oscillation frequency of 11.45 MHz.
Seiche: A seiche is a standing wave that oscillates in a semi-enclosed or fully enclosed body of water, such as lakes, bays, swimming pools, or ocean harbours.
Causes: Strong winds or rapid changes in atmospheric pressure push water from one side of the water body to the other. When the wind stops, water rebounds and oscillates back and forth.
Other Triggers: Earthquakes, Tsunamis and Severe Storm Fronts
Characteristics:
Oscillation: Water continues to slosh back and forth for hours or even days after the initial trigger.
Occurrence: Happens in enclosed or semi-enclosed water bodies like lakes, bays, and ocean shelves.
Seismic Waves Across the Planet: The landslide’s energy rang the Earth’s surface, creating seismic waves that were detected globally. These waves matched the strange, single-frequency seismic signatures recorded by stations, confirming the landslide as the source.
About Seismic Waves: There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves.
Body waves can travel through the earth’s inner layers, but surface waves can only move along the surface of the planet like ripples on water
The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave, and, consequently, the first to ‘arrive’ at a seismic station. The P wave can move through solid rock and fluids,like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air.
The second type of body wave is the S wave or secondary wave, which is the second wave felt in an earthquake. An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium. It is this property of S waves that led seismologists to conclude that the Earth’s outer core is a liquid.
S waves move rock particles up and down, or side-to-side–perpendicular to the direction that the wave is traveling in (the direction of wave propagation)