Observed Geologic Hazards in Costa Rica
(written by a student in Geology 201 - quarter version of GEOL 2010 - 3/31/97)
First of all, my trip to Costa Rica was a success. We traveled throughout a great deal of the country visiting rural agricultural cooperatives. I had the opportunity to visit the area surrounding Arenal, the San Jose basin and the Osa Peninsula. By now you must realize the number of hazards I witnessed. I will stick to those that seemed most significant. I’ll begin with the Meseta Central.
The San Jose basin was much more developed than I had pictured before arrival. There was a great deal of work done on the infrastructure in the last ten years. Unfortunately, a great deal of this work was commissioned in marginal areas. The most glaring example was the large tract of highway built along the mountains. Much of it was cracked or crumbling due to weather; high use; and, most importantly, location.
The road was built across the continental divide, much of it on slopes. When the road was being constructed, a large amount of material was removed which destabilized the mountain. The result has been the continual damage and destruction of portions of the road. I witnessed many places where the outside land of the highway had broken and been carried down the mountain. I’m just glad it didn’t happen while I was on the road. Rather than stabilize the road, officials send out crews to repair the holes and gaps created. I did see one project to reroute the road in a less dangerous area.
In addition to the destruction of the road itself, landslides are a serious hazard on the same highways. When the weather turns wet, April-December, the slopes above the road gain weight and the road is inevitably blocked by fallen material.
The second most prevalent hazard I observed was the large amount of erosion being caused by large-scale deforestation. This was a problem everywhere I traveled but seemed most intense in the Guanacaste region. There, large ranching and farming operations have cleared huge tracts of land to increase production. The problem they have caused is the filling of river channels which increases the likelihood and effects of floods. I did not see any flooding while I was there but I can imagine it to be similar to the conditions found in Kentucky in March. I was also able to view the effects of gold mining on a river.
Near Corcovado National Park on the Osa Peninsula, the Rincon River is a prime gold mining area. It was mined commercially until the government banned the practice. Now, some of the former employees of the cooperative that did the mining continue illegally, on their own. Their methods are particularly damaging to the river and its surroundings.
Small-scale gold mining, panning, requires that a small channel be constructed to increase the flow and velocity of water. The miners achieve this by diverting the river through a series of man-made sluices. The result on the river is a change in direction, speed, and erosion. To compound the problem, a small group of buildings has been constructed on the floodplain. While the people are aware of the problems they seem unwilling to move. They state that when the area floods they move until the river backs off.
The miners also cut run-off "mines" in the side of the hills. The idea is that when it rains material from the hill is transported to the river which then flows through the sluices, increasing the amount of gold removed. Of course the unused material is left in the channel adding to the natural load. Evidence of mining can sometimes be seen as far as a half-mile downstream from an active site.
The hazards I have discussed so far are those which cause the most damage year after year. I was also able to view those hazards which spring to the mind of most people. Namely, volcanoes and earthquakes. The former are scattered throughout the country along the center running north/south. The latter I was able to see in Cartago, near San Jose.
While in the country I visited two volcanoes, Arenal and Irazu. My visit to volcan Arenal was lackluster at best. The two days I was in the area the sky was cloudy and I only saw the base of the mountain. However, I did speak to a couple who saw the volcano later and were amazed by the amount of activity. This mountain is relatively active almost every day, sending out lava and volcanic bombs constantly. Luckily the rate is fairly low and poses no threat to the surrounding communities, yet. Irazu is a different animal.
I was able to visit the top of volcan Irazu on a clear day. It is possible top view three separate craters from that vantage point. Irazu is not as active as Arenal but when it is I don’t want to be very close. I heard a story about two scientists studying the mountain who were killed by an ash cloud that suddenly changed direction taking them by surprise. The volcano is currently home to dozens of research stations used to study volcanism and tectonic activity.
During the same journey that took me to Irazu, I also visited Cartago and the site of a number of earthquakes. Until 1910, a number of attempts were made to construct a large cathedral near the center of the city. However, each time it was built or repaired another quake destroyed it. Finally, in 1910, the government decided not to rebuild and the rubble still remains today as a reminder of the power of earthquakes. The city also remains relatively small today because of the continued effects of quakes. San Jose is less active and has grown instead.
I could continue but most of the hazards I saw were related to erosion and landslides. Since I have already covered some of the larger effects I witnessed I won’t belabor the point.