Glaciers can play an important role in landscape dynamics, interacting with other factors to shape landscape development. Two days after a 7.8 magnitude earthquake struck North Canterbury, New Zealand, a landslide occurred between nearby Fox and Franz Josef glaciers. This landslide could offer insight into the role of glaciers in seismically active areas, particularly concerning the ways in which glaciers interact with earthquake-related instabilities in the landscape.
The landslide occurred at Omoeroa at around 2 p.m. (GMT +12 hours) on November 16th, closing off a section of State Highway 6 along the west coast of South Island for about three hours until debris were cleared.
— NZTA Canterbury/WC (@NZTACWC) November 16, 2016
Earthquakes and landslides are common in New Zealand due to the country’s location on the Pacific Ring of Fire, the area around the Pacific Ocean that is very seismically active. It is so named because of the prevalence of volcanic activity within the ring, which is made up by the major tectonic plate boundaries.
Earthquakes, which occur when Earth’s crust breaks along faults (fractures in the crust), send tremors outwards from the point of breakage. This particular earthquake was caused by oblique-reverse faulting (faulting that had both strike-slip and reverse components) near the boundary of the Pacific and Australian tectonic plates. Landslides, like the one that occurred between the two glaciers, are often triggered by other natural disasters, such as earthquakes or floods. In this case, the earthquake and its aftershocks triggered up to 100,000 landslides, causing local damage and blocking major roads and railway routes.
In conversation with GlacierHub, Umesh Haritashya, an associate professor in environmental geology at the University of Dayton, explained that the region in which the landslide occurred is prone to landslides even without any seismic activity. This is due to the topography of New Zealand’s Southern Alps. As such, it would not be surprising if the earthquake, landslide and glaciers are connected, he said.
While the two glaciers are found on the west coast of South Island, the earthquake occurred on the east coast of the island. The distance between the two suggests that the intensity of the tremors experienced in the area around the landslide may have been quite low. Nonetheless, a link is possible, according to Jeff Kargel, a geoscientist at the University of Arizona. “The timing of this big landslide is certainly suggestive of a direct link to the earthquake,” Kargel told GlacierHub.
“For both direct and circumstantial reasons, earthquakes, glaciers and landslides are closely associated,” Kargel explained. “There is the direct influence of glaciers that produce lots of unstable rock debris over thousands of years, and there are indirect influences, where glaciers erode the mountain topography and produce very steep slopes. These factors create conditions under which seismic activity can easily set off landslides.”
In addition, Kargel noted that glaciers occur where uplift rates have been high and the terrain is elevated to begin with. This means that either circumstantially or indirectly, glaciers and landslides can occur nearby.
Kargel further stated that large earthquakes tend to create instabilities in the landscape that are later exploited by natural processes, making landslides more frequent in the aftermath of earthquakes. “The spike in landslide activity can last for several years,” he said.
In addition to seismic activity, other causes like heavy rain after the earthquake could have contributed to the occurrence of the landslide. New Zealand’s MetService reported that the areas of the glaciers had received considerable rain, with 80-120mm falling the night after the earthquake.
“The West Coast receives an unusually high amount of rain, so slopes are already reconditioned and any seismic activity can trigger major landslides,” Haritashya explained.
The links between the earthquake, glaciers and landslides will become clearer as scientists examine similar events more fully. For now, landslides like these offer an insight into the complex interactions between glaciers, topography and seismic activity. Earthquakes can cause large amounts of disruption to people’s lives, so advancements in this field of science could prove valuable to communities as they seek to address the challenges posed by natural disasters.