A landslip or a landslide is a phenomenon that is geological which entails a variety of ground movements like rock fall, shallow flow of debris, and deep failure of slopes which may occur in coastal, onshore or offshore environment. The major reasons causing landslides are gravity and slope instability. The instability of the slope may be caused by various factors like erosion, earthquakes, volcanic eruption, groundwater pressure or lack of vegetative cover.
One of the types of the landslide is the mudslide. This is moving of rivers of soil, rocks and water. They are just like the other landslides but mostly are due to storms. They are also referred to as slurries, mudflows or landslides. Debris moved by the mudslide can travel several miles from the point they were before the slide. In U.S.A the prone areas to landslides are Puerto Rico, Utah, Tennessee, California and Kentucky.
One of the recent times mudslides, happened on January 11 2011 in state of Reo de Jeneiro which is in Brazil. The mudslide was triggered by heavy rains that occurred mostly in Teresopolis, Sumidouro, SanJose do Vale do Rio Preto and Nova Friburgo. It is estimated the death toll was about 900 mostly occurring in Teresopolis and Nova Friburgo cities. It was claimed that this was the second worst natural disaster which is related to weather to ever occur in the history of Brazil. The other one occurred in 1967 which ended up killing 1700 people. Also in January and April 2010 heavy floods and mudslides occurred in the same area and also in 2009(Barbassa, 2011).
The rains that occurred on the first week were more than the rains expected for the whole season. The place is said to be prone of small mudslides due to its hilly landscape. The steep landscapes covered with roam weak soil and the continued degradation of the vegetation caused the mud slide to be worse. Moreover, many buildings built of the sides of the hills caused the land to become more unstable and with the heavy tropical rains that poured, the mudslide was horrific.
Rio de Janeiro is full of volcanic rocks which in most times were formed very first as the lava cooled hence they are weak rocks that are disintegrated and with many cracks due to the interchange of hot and cold weather in the region. The soil entail roam soil that is thickened by the dense tropical forest that covers most part of this state. Moreover, the continuous human factors like quarrying in the area has made the rocks structure to be more weak(Staff, 2011).
The environmental effects of the mudslide were as follows. Foremost, many trees found on the hills were uprooted leaving many areas bare with no trees to cover. Second, the rich roam soil was carried from the farming land and deposited into rivers, towns or in the ocean. This left unfertile and rocky land where even vegetation could not grow. Lastly, the heavy rains that washed even sewages and dumpsite led to pollution of water in rivers and oceans leading to death of water living animals like fish(Domit, 2011).
The reason behind the occurrence of the mudflow in this area is when the pore pressure in the soil that is fine grained is increased until the weight of the soil which is supported by water pores goes on decreasing creating an internal strength that is shearing to the material. This brings about a bulging lobe which starts to move in a rolling, slow motion. During the motion, the lobes spread out increasing the drainage of the mass thereby lowering the velocity of the entire flow. This causes thickening of the flow. They mostly occur when the soil is greatly saturated with water that increases the pressure in the pores of the soil(Easterbrook, 1999).
Due to the increased mudslides in the area, and a move to avoid greater damage and loss in these state, the Brazilian government has started taking measures to prevent mudslides in the next heavy tropical rains. They have done this by building gabions that surround all those prone areas and have even put measures by preventing building of more houses and buildings on the slopes or at the foot of the hills. With this, the losses of lives that are occurring after every mudslide are expected to decrease.