A 100-meter-deep (330-foot-deep) sinkhole killed two teenage siblings and swallowed about a dozen homes, forcing the evacuation of nearly 1,000 people in a crowded Guatemala City neighborhood. Officials blamed recent rains and an underground sewage flow from a ruptured main for opening up the sinkhole on Friday, and warned that it could widen. The two bodies were found near the enormous fissure, floating in a river of sewage. The pit emitted foul odors, loud noises and tremors, shaking the surrounding ground. A rush of water could be heard from its depths, and authorities feared it could widen or others could open up. "We have closed the valves on the storm and sewer drains and we are going to wait until the area stabilizes before going down there to evaluate, but in the meantime the mouth of the hole will certainly become larger," said Alvaro Rodas, the director of social development for Guatemala City. Edward Ramirez, 26, said he and other residents had been hearing noises and feeling tremors for about a month before the sinkhole appeared before dawn, waking many in the poor neighborhood. "People were shouting 'The electric posts are falling down!'" said Ramirez, who lives 50 meters (50 yards) from the hole. "We are going to a friend's house now. There's no way we'll stay here."
Emergency spokesman Juan Carlos Bolanos identified the dead teens as Irma and David Soyos. Their father, Domingo, was still missing, according to national disaster coordinator Hugo Hernandez. Residents said others were unaccounted for, but Hernandez could not confirm that. Authorities evacuated nearby homes and cordoned off a 500-meter (500-yard) perimeter around the crater. Police helped residents move out, with some officers carrying refrigerators and televisions on their shoulders while other pushed sofas on makeshift carts. Security officials were on guard for possible looters and to clear the area of onlookers. Authorities had apparently suspected something was wrong with the site before the sinkhole appeared. "We knew, and (the seismology institute) had placed a seismic meter there," Rodas said. "The city government had contracted a robotic camera system to go down there, but the disaster occurred first." Cristobal Colon, a spokesman for the municipal water authority, said the sewage main ruptured after becoming clogged. He said the army had been considering a controlled explosion to clear the pipe, which carries both rainwater and sewage for much of the capital. Antonio Fuentes, 50, said he plans to abandon the run-down neighborhood he has called home for 15 years. "Last night a friend had to take my handicapped wife out on motorcycle," he said. "Now I'm leaving for good, never to come back."
The valley of Guatemala
Environment and history
The city of Guatemala, the national capital of the Republic of Guatemala, is by far the most prominent city in the country. It is located in a high valley on the Guatemalan volcanic plateau, at an elevation of 1 800 m above sea level.
Before Europeans conquered the country, the Guatemalan highlands were already densely populated by a civilization, whose economy, like that of the Mexican indigenous peoples, was based on the cultivation of com, chili peppers, tomatoes, and other local crops. When the Spanish arrived, the highlands region was inhabited by the Cakchikel nation of the Mayan group, with their capital in Iximche. As they had done in Mexico, the Spanish conquerors established their capital (in 1523) on the same site as the existing one. Iximche was about 100 km west of and at a higher elevation (about 2 000 m) than the present Guatemala City.
In 1527, after a destructive earthquake, the city was moved to a site about 80 km to the east at a lower elevation (1 530 m). The new city, Santiago de los Caballeros, was established at what is now Antigua. This site is at the foot of a high volcano (the Volcan de Agua) whose main crater contains a lake. In 1533, the Volcan de Agua erupted. The lake caused a flood and a mudflow destroyed and buried large sections of the city. Several hundred people died and most buildings were demolished.
In 1543, the city was rebuilt in the same valley, but was again destroyed by an earthquake in 1773. In 1776, it was established at its present location and named Nueva Guatemala de La Asunción. The old city was gradually rebuilt and today it is a medium-sized city of about 50 000 people (Antigua).
Guatemala City, which remained the capital of the colonial Capitania General de Guatemala, became the capital of the independent Republic of Guatemala in 1837. The city has grown from tens of thousands of inhabitants at the beginning of the 20th century to the current 1.5 million people, with all the requirements and strains on the environment that accompany accelerated urban growth.
The Guatemalan highlands are in an area of volcanic and seismic activity (Fig. 18 ). Twenty large volcanic cones, with elevations ranging from 2 000 to 4 220 m, and several hundred smaller ones dot the southern mountainous areas of the country. Volcanic eruptions and related seismic activity are common, and recent geology and geomorphologic development are closely tied to these phenomena.
The climate of the highlands is subhumid to humid, with annual precipitation ranging from about 1 000 mm in the drier north-facing slopes to more than 2 000 mm in the south. In the city of Guatemala itself, annual rainfall averages 1300–1500 mm, concentrated in the summer (June to September). Natural vegetation is deciduous forest up to 2 200 m and coniferous forest above this altitude. This forest was partly cleared (even during pre-Hispanic times) to make room for agriculture. This process has continued and has accelerated during the last few years. Today, the forests of the highlands have been reduced to small pockets on the steeper slopes that are not suitable for farming.
Fig. 18. Aerial view of the Guatemalan highlands.
Geology and geomorphology of the valley
The geology of the Guatemala valley is relatively complex (Fig. 19). Over a base of Cretaceous limestones and plutonic rocks, intense and prolonged volcanic activity gave rise to large accumulations of various volcanic rocks and associated deposits.
The valley is an elongated depression oriented in a north-northeast to south-southwest direction. Water flows both northward and southward from a portion of the continental divide that lies more or less perpendicular to the main axis of the valley.
A large lake (Amatitlán) has formed in the southern part of the valley, because of volcanic obstruction of run-off. It is drained by the Michatoya River, which flows to the Pacific Ocean. The northward flowing rivers (Las Vacas and its tributaries El Zapote and Tzalja) drain the smaller northern part of the valley toward the Caribbean sea.
Volcanic cones surround the city, the largest ones being the Volcan de Agua, about 20 km southwest of the city, whose summit is over 3 000 m above sea level; and the Pataya, about the same distance to the south, with an elevation slightly above 2 000 m. The valley is a large graben with locally intercalated horsts. Both the elevated and depressed areas are composed of volcanic rocks, although older limestones are found in the Las Vacas River in the northern part of the valley.
The oldest formation identified in the Guatemala valley is a calcareous unit of fractured limestones in the Las Vacas basin, with limited outcropping. Overlying the Las Vacas limestones, a thick sequence of lava flows and associated deposits of Tertiary age are encountered. These lavas are heavily fractured, resulting in high secondary porosity. The Tertiary lavas are covered by two sequences of fluviolacustrine and volcanic deposits of Quaternary age:
* A sequence of fluvio-lacustrine deposits, composed of volcanic materials alluvially reworked and deposited in river beds and plains or in lakes. Their thickness does not exceed 100 m. The alluvial sediments have a relatively high permeability, but the lacustrine deposits can act as aquitards or aquicludes.
Fig. 19. Cross-section of the Guatemala valley, showing geological formations of the region.
* A sequence of volcanic deposits, formed by a large accumulation of pyroclastic products including ash-flow tuffs. These materials have a wide range of consolidation levels, from loose to well-compressed. The maximum thickness of this formation exceeds 200 m. It is moderately to highly porous and contains an excellent aquifer, which is heavily used.
Guatemala City gets 80% of its water from groundwater sources; this amount probably represents the maximum obtainable from these aquifers. Of the 5 m3/second required by the city (somewhat higher during peak periods), up to 4 m3/second comes from 200 wells distributed throughout the valley. The remaining 1 m3/second is obtained from surface sources outside the local valley.
A pipeline was built to bring river water into the city. Its capacity is 2.5 m3/second, although current flow is less than half of this. There are plans to build a battery of wells in the volcanic aquifer at Antigua to augment the volume transported by the pipeline. The only other surface water available is in Lake Amatithin, which is heavily polluted.
Because recharge of the aquifers takes place mainly in urban and suburban areas, strict controls are required to avoid degradation of the groundwater. Currently, controls are virtually nonexistent. However, decision-makers will have to remedy this situation, because Guatemala cannot afford to lose this key resource through lack of adequate protection or planning.
How do sinkholes form?
How Sinkholes FormSinkholes are most commonly thought of as physical depressions or holes in the surface of the land. Not all sinkholes, however, are as visible or dramatic as a home or roadway falling into the ground. Many times, sinkhole activity never manifests itself of the surface of the land, making it harder to detect.
The entire state of Florida sits on top of thousands of feet of limestone. Limestone is a porous rock, capable of cracking, breaking, and dissolving. The most significant factor in the development of sinkholes is the dissolution of the limestone underlying Florida by acidic waters. As water moves through the soil, it becomes more acidic as it reacts with living and decaying plant matter. This water reaches the underlying limestone, it slowly begins to dissolve the rock and creates voids and cavities. The soil resting on top of the limestone then collapse or subsides into the caverns and voids and causes sinkholes.
A rapid increase in sinkhole activity can be attributed to the development of land, which changes the earth’s surface as well as the weight or load on the soil beneath it. The creation of retention ponds, new buildings and homes, roadways, and changes in ground water levels can all trigger sinkhole activity.