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Scientists Are Not Happy How Media Reported The Kenya Crack

It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.
Sherlock Holmes

The story of a large chasm opening suddenly in Kenya’s Narok and Suswa County, damaging a major road and several houses, got quickly viral. The story was first reported around March 22, four day after the first fissure occurred, and picked up by international media around March 29, quickly spreading thereafter on the internet.

Reuters/Thomas Mukoya

A man takes a selfie in front of the large crack formed in March 2018 in Narok County.

 

The proposed explanation that the fissure is evidence of Africa splitting apart, driven by mysterious tectonic forces deep within, sure is appealing. However, there is quite some controversy surrounding the nature of the chasm. In the first reports it was suggested that it is a fault. Some news reported that the opening of the crack was preceded by seismic activity. However, this area is poorly covered by seismograph stations and also no international station picked up an especially strong earthquake in the region, so this claim seems to be unverified at the moment. It could be a fossil fault, not active anymore and covered by sediments, washed away by the recent strong rainfalls. Mount Longonot and Mount Suswa, two dormant volcanoes, are located approximately ten miles away and the area is part of the Great Rift, a very large tectonic structure stretching almost 1,900 miles from the Gulf of Aden in the north towards Zimbabwe in the south. Here slow tectonic movements, less than one inch per year, slowly deform the rocks. Also, uprising magma, associated with the volcanoes, can deform rocks and cause faults. Along such faults, the rocks break and the continuous movements along the faults grind the rock into pieces. Faults are often filled with broken rocks and running water, following the path of least resistance, tends to excavate and erode this material.

Google Earth images show some linear structures visible on the ground, suggesting that indeed more erodible material was located there, quickly removed by the recent rainfalls and forming a gully into the unconsolidated material (mostly volcanic ash deposited by the nearby volcanoes).

Temblor/David Jacobson

This Google Earth image shows the location of the collapsed road near the town of Mai Mahiu, just east of Nairobi. This photo also appears to show evidence of the crack, which is pointed out by the red arrows. The linear feature appears to match the orientation of the crack in the photo above. Image and caption from the blog temblor.

 

However, seismologists noted, commenting the news on Twitter with the hashtag #KenyaCrack,  that the chasm doesn’t really look like a typical fault rupture. The idea that a large fissure opens during an earthquake is more an urban legend. In most cases, as earthquakes are associated with compressive forces, a block will move along a fault plane, forming steps or escarpments where the fault intersects with the surface. Like this example of the Wall of Waiau, formed by the 14 November 2016 Kaikoura earthquake in New Zealand.

Kate Pedley

Wall of Waiau, a fault trace escarpment formed by the November 14, 2016 Kaikoura earthquake in New Zealand.

 

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