The Venezuela mass movement event was a series of mudslides and landslides resulting from a series of floods in December 1999.There was many causes to this, some being human and some being more physical causes like heavy rainfall. This effected most settlements in the state of Vargas the largest of which being Caracas. It was the combination of these two things, a natural event being the mud and landslides and the vulnerable population in Vargas, many of which were living in shanty towns making them particularly vulnerable which made the event into a hazard and disaster. This can clearly be shown by Dregg’s model. As is clear from the first diagram that when the natural event does not affect people in anyway (shown as the two circles do not touch) then it is only called an event and no loss of any kind is observed. However when the people are affected by the event and in the case of Venezuela this effect was very large with many of the people defenceless in shanty town accommodation as well as living in a crowded and dense and living near in the shadow of the mountain. All of this meant a large interaction between the event and the vulnerable non resilient population creating the disaster.

There were a number of physical causes to the event of both climatological and geomorphical nature. The largest cause of all and the trigger for the slides is the heavy rainfall in the weeks and days especially before the event. As can be seen by the graph, December had been an unusually wet month, the wettest December for 100 years with 914mm of rainfall from the 9th to the 18th just after the slides. The trigger was the found on the 14th and 15th were there was 120mm and 380mm respectively which triggered the slides. All of this heavy rainfall caused the landslides because when the water infiltrated into the soil on top of Mount Avila and surrounding hills before some would have percolated further into the soil. This rainfall would have added a lot of weight to the cliffs of the mountains and surrounding hills. This would then mean that the increased weight would increase the shear stress (stress allowing material to move) which would have been a contributory factor for causing the mass movement when the sheer stress would have been larger than the sheer strength holding the slopes on the mountains together leading to the mass movement. This led to some of the very serious effects of the event, where in human terms 50,000 people died and 40,000 were made homeless. Other primary impacts included 90,000 homes being destroyed. Added to this was just a severe secondary impacts which disease breakouts such as cholera claiming many more lives Heavy rainfall beforehand was the trigger for the event and was probably the largest physical factor with the amount of extra stress, if not the largest overall.
Other physical factors were very important, one of these being geomorphology. This was very important for 2 reasons. The first of these is the very steep slopes of Mount Avila and the surrounding mountains. These mountains, the northern most part of the Andes Mountains also called the Cordillera de la Costa are known for being very close to the coast, just 10km sometimes. This means that the slopes have to be very steep in order to get from 2000-2700m to sea level in just 10km. These steep slopes were again contributory in the mass movement. This is because steep slopes (especially those above 35 degrees like much of the landscape in the region)are especially unstable. This ‘freeface’ surface is particularly unstable because a steeper surface has less support from the surrounding material and means that the gravity acting on it can have a larger effect as it has less support. This would increase the stress on the rock, however this is not as important factor as the heavy rainfall as even with these extra stresses that the slope caused in the past had not been enough to cause mass movement and instead the mountains slopes were still in equilibrium and so it is contributory, it cannot be as important as heavy rainfall as without the rainfall the stresses would not have been high enough. However it could be argued that the severity of the slopes and the height of the mountains in relation to the sea level so near could easily have led to the rainfall being so large in the first place via relief rain. This is when moisture which is in the air being blown by the wind in an onshore wind would have been pushed over these mountains and cooled, condensed and become heavy enough to fall as rain and the relief rain effect would have led to their being more rainfall falling at the top of the mountains which would have led to more stress and a larger mass movement event.
Geomorphology was also important with the type of rock. The Andes Mountains in the region are made up of igneous rocks which have been deeply weathered over millions of years and now a lot of eroded clay is found by streams which have been eroded by the water over the same time frame. This meant that a lot of loose material was around at the time simply resting on the mountains and just a small amount of mountain face collapsed it would have moved and forced other detached pieces of rock down the rock with it and it would have made perhaps a small rockfall into the large mass movement. This would have been very important as without it it may not have become a major mass movement event that killed 30,000 people and it instead may have just been a small rockfall so these detached rocks and the fact they could clump together with momentum to make a mass movement event was very important. Overall from all the physical factors it can be said that the heavy rainfall was the most important as it triggered the event and that the steepness of the slopes was the least important.
Human factors as well as physical factors were important. One of the human factors that is very important is deforestation. This had been done in order to make way for shanty housing as the population of the area grew in many slum areas. This had effects both long and short terms in aiding the devastation of the event. In the long term beforehand the fact there were very few trees remaining on the hillsides and this meant the dense leave could not intercept the common rainfall in Venezuela, often in thundery showers, and then either have it lose water back to the skies via evapotranspiration. Also the roots of the trees would have taken up water making the ground less saturated and more able to be infiltrated. This would have meant that much less water would have hit the ground and acted an overland excess water flow. This running water in the surface would have led to more erosion through processes like hydraulic action when the force of the water breaks the rocks and this would have led to more detached and broken up material on the surface. Also in the short term in the days of the landslides when overall 914mm of rain fell it meant that more rain flowed as overland excess meaning that with more water it would have had more competence to pick up more material to create large mudslides.
Another human factor was land use. Around 700,000 people live in the surrounding area in 1999 including Caracas and this area has been built up with a massive urban sprawl of shanty towns building up in the area and on hillsides and the new roads and other impermeable surfaces that were built around the area, especially on the ever urban hillsides. This massive % increase of urban land cover, most of it shanty towns without proper drainage systems mean that there were many more impermeable surfaces in the area. This means that when all the rain fell over a very short period of time ( mainly 13th, 14th and 15th of December) any rain that fell of this new impermeable surfaces could no longer percolate into the soil, creating more surface run off fuelling the mudslides. This led to perhaps the impacts being more severe with many homes destroyed, roads, and highways and damaged airports all primary impacts. Discounting human loss, economic loss alone was damaged at 3 billion dollars. This is especially a human factor as it is known to be a fault of former government not to remove these informal settlements. So it is clear both land use and deforestation are both very important and although they were both definitely not as important as the physical factors which truly triggered the event, it is clear that these two factors only exasperated the event and made it a much larger event as the water could not drain.
The government’s failures before and after the event also contributed to the risks. Before the event the government had had warning that a major natural event could be about to happen. They were warned by weather forecast models in the days before hand and by sediment building up in river channels in the mountains, a clear sign of the slides that were to come. Despite this they failed to remove people, especially from the most vulnerable areas such as those in shanty towns and in alluvial fans. If they could have removed the most vulnerable, which clearly the area had capacity for as 100,000 people were moved to temporary housing after the disaster clearly shown this was a major government area. The government response also has to be questioned in the short term. The government simply created a relatively small, without external help of any kind, search and rescue mission for the area and also had a small relief operation without using aid from other countries. This was again a major factors in the risks from the disaster being very large as it was ineffective and made the secondary impacts very large indeed with malnutrition, disease etc. being rife and leading to many more deaths. There is also blame to be laid at the government for even allowing people to build shanty towns at all in the first place as it was always going to leave them very vulnerable to events such as the ’99 slides and the government did not even make sure they had some sort of defence to it such a a good drainage system. Government corruption has been blamed for this. This is by far the most influential human factor as although the government could not have reduced the size of the event or stopped it happening all together, they could have stopped it from be a human natural disaster with the loss of so many lives so really the risks of the event were vastly increase by the incompetence of the government and this was really the reason it because such a widespread major disaster. vOverall it is clear that the physical factors are the most important in creating the risks associated with the Venezuelan mud and landslides as the physical factors are the only factors that actually made the event happen, human factors did not cause this. Of the physical factors it is clear heavy rainfall is the most important as this was the trigger for the slides and without this they would not have happened. The human factors did increase the risks though, especially the government’s incompetence both before and after the even resulting in the loss of many lives for little reason. Other human factors helped increase the risks by increasing the size of the event too but as these factors did not actually start the event like the physical factors, they cannot be called as important in making the Venezuelan mass movement event so risky.