Chile is a country characterized by its seismic activity. While the earth often surprises us with seismic tremors, the question is, do the glaciers shake? The answer is yes.
Cryoseismology is an area of study that is destinated to research the origin of glacier seismicity (either on the base, inside, or on the surface of the glacier). This area of research started developing formally in the early XXI mainly with the use of seismic methods designed originally for studies in solid ground. But in this case, it’s applied on ice. Despite its recent creation, the quantity of scientific publications related to this area has confirmed the growing interest of the scientific community. It has highlighted the importance of studying these events.
The study of cryo-seismology has allowed us to identify the main types of glacial earthquakes and the processes capable of causing them; one of the main processes that produces glacial earthquakes is the formation of cracks on the surface of a glacier. The earthquakes associated with the formation of cracks are dominant in glaciers with a high degree of melting and are located on steep land. Although earthquakes related to crack formation can be frequent in these glaciers, their extent is local, and their magnitude generally doesn’t exceed the unit on the seismic moment magnitude (Mw) scale (Podolskiy & Walter, 2016). The study of these events not only allows to identify the formation and propagation of cracks, but also provides valuable information on the degree of stability of a glacier on land.
Glacier with cracks in it. Cordillera Andes / © Camilo Rada
A second mechanism capable of generating glacial earthquakes is related to how the glacier flows (Kanao, 2018). The presence of fluids or sediments saturated with water at the glacier’s base allows it to slide on the surface on which it lies. When sliding, the glacier may do so continuously or moderately. In general, a uniform base will allow the glacier to flow continuously, while an irregular base will interrupt the flow of ice. In this case, roughness in the land can act as a brake on glacial flow. By slowing the flow, these points can store energy which will be released suddenly when their resistance threshold is exceeded. Once this happens, the accumulated energy is released in the form of seismic waves, and the glacier slides considerably until it’s again stopped by other roughness. Generally, these events don’t present magnitudes above Mw=3 (Podolskiy & Walter, 2016). The study of these earthquakes contributes to the study of glacier dynamics and how the glacier interacts with the base on which it’s emplaced (Kanao, 2018).
A third mechanism that generates glacial earthquakes is the “calving” of a body of water in the terminal zone of the glacier. These events can last several minutes and reach magnitudes of up to Mw= 5.1. There are also other mechanisms capable of generating glacial earthquakes, these include the occurrence of hydro-fracturing produced by liquid water flows within the glacier and the emptying of glacial lakes (either on, within, or under a glacier), among others.
In general, earthquakes of glacial origin don’t generate significant surface movement or vibration because the energy is dissipated during an earthquake. Therefore, their occurrence doesn’t trigger a direct threat to humans or buildings. However, glacial earthquakes can be indicators of increasing internal instability, which in some cases can lead to devastating events. These include the craving from hanging glaciers which can move down the valley at high speeds. Because of this, seismic monitoring of glaciers has proven to be a valuable tool for predicting the occurrence of ice block cravings. It has been observed that earthquakes increase up to 10 times more before a craving event than during a period of no breakup.
The generation of glacial earthquakes is directly related to how a glacier interacts with its environment. Therefore, the study of cryo-seismology not only provides an important tool to understand how they interact but also to monitor their stability. Even more so in the current context of climate change in which the stability of glaciers is more affected, either by the increase in the formation of cracks, the increase of fluids at the base triggering the slide, or the alteration of the internal structure of the ice and firn. The latter highlights the necessity to identify glaciers in unstable conditions, which may present a potential threat to both mountain communities and critical infrastructure such as mountain reservoirs. The formation of a seismic monitoring network will allow us to know better a glacier’s stability and thus, anticipate the occurrence of potentially catastrophic events.
Referencies
- Podolskiy, E. A., & Walter, F. (2016). Cryoseismology. Reviews of Geophysics, 54(4), 708-758.
- Kanao, M. (2018a). A Decade of Advances in Cryoseismology. In Polar Seismology-Advances and Impact. IntechOpen.
- Kanao, M. (2018b). A New Trend in Cryoseismology: A Proxy for Detecting the Polar Surface Environment. Polar Seismology: Advances and Impact, 75.
Highlighted image:
- Glaciar agrietado en zona frontal, frente en agua. [Cracked glacier in its frontal zone] Peninsula Antártica [Antarctic Peninsula] / © Dieter Tetzner. Link ubicación [Ubication link]
