19 October 2008

A strange report from Nigeria…

Posted by Dave Petley

The Nigerian newspaper “The Punch” has been carrying a quite strange and intriguing story over the last few days regarding an apparently huge landslide in the Awgu area (i.e. at about 6.0046N, 7.4024E). The key points of the story (from the Punch) are:

“Residents of Ugwueme, Umuhu, Ugulesi Awgu and Ezinese Mgbidi communities in Awgu Local Government Area, Enugu State could not believe their eyes when they visited their farmland in the morning. Expansive farmlands measuring more than 20 square kilometres had been destroyed by a tremor. On account of the incident which was later explained as a landslide, there were huge cracks and depressions on the land as if a straying ballistic missile had exploded there. Some trees sank in the depression while others were completely uprooted.”

The traditional Prime Minister of Awgu, Chief Stephen Onuorah, who visited the scene on the second day of the incident, said he felt a massive shaking and reverberations under his feet. He said he heard a noise that sounded like the roaring of a bulldozer. Surmising that it was an earthquake, he contacted the Chairman of Awgu Local Government Area, Chief Uche Anioke, who later led some officials to the site. Amazed at the level of devastation, the council boss contacted experts from the Federal Ministry of Mines and Steel Development, but the confusion over the incident was dispelled by the team of experts from the National Geo-hazards Monitoring Centre led by the director of the agency, Mr. Alex Nwegbu, and Prof Cornelius Nwajide, a lecturer at the University of Nigeria, Nsukka and consultant to Shell Petroleum Development Corporation.

The team which also included geologists, geophysicists and seismists, visited the farmland on Tuesday. They described the incident as a landslide which occurred on account of massive rainfall which “peculated into the land to an impermeable layer and caused land cracks”. Nwegbu in his preliminary report traced the remote cause of the incident to the geographical positioning of Awgu which was sitting on a ridge belt called clay star. The belt runs from Idah in Kogi State through Awgu to Arochukwu community in Cross River State, all of which are prone to geo-hazards.

The Chairman of the House Committee on Petroleum Resources and Environmental Management, Chris Ugwu, in a report sent to the state assembly, described the incident as an unusual disaster…Ugwu said that his committee, which visited the area, observed that large portions of land were compressed into crooked ridges and valleys.”

This is intriguing because the area affected appears to be very large (>20 square kilometres) and the level of destruction appears to be high, even though the landslide has not been catastrophic in terms of movement. The terrain is question is not particularly steep or rugged, and this is not an area with notable seismicity. I would be very interested to hear more about this slide. I wonder whether this earlier report, although possibly covering a different area, might provide an indication of the root cause of the issue?

Although Nanka has bared the brunt of the erosion-based devastations, it has however not been relegated only to Nanka. Other towns have been faced with their unfortunate share of these hellish gullies. Enugu Ukwu is another town ravished by gully erosion. According to a 1993 State report on the state of gully erosions in Anambra, “the number of gullies presently pervading and ravaging the lands of Enugu Ukwu defies solution”. The story of the gullies in Enugu Ukwu begins with the Etti-Umuatulu-Osili Enugu Ukwu gully networks which starts from Etti Awobu village and gallops down a slope stretching down into Umuatulu Awobu where it splits into two branches; to run into Obuagu Osili where it converges to a point where the gully depth stands at about 80meters. The gully network within the Urukpaleke and Akama Osili areas originate which is reported to have been aggravated by a flood from a faulty drainage line constructed along Enugu-Onitsha road. The same gully stretches to another Akama Osili village and joins Urukpaleke gully. According to Inter Press Service New Agency who was one of the many New Agencies that reported on the incident, “the inhabitants of Umuchiana, one of the villages that make up Ekwulobia community in Anambra state, were woken up at night by a noise only to find some houses at the edge of the village giving way to landslide. They deserted their homes, taking refuge in nearby forest and villages. By the time they returned to their village the following morning, several houses, a church and some roads were washed away. Their farmlands, palm and cashew trees were not spared either. Though nobody died in the incident, more than 250 families (made up of more than 1,500 persons) were displaced.