El Salvador's geography: a country built on its volcanoes

Why the capital sits between two volcanoes

San Salvador stands on the central plateau at 682 metres, with the San Salvador volcano above it and Lake Ilopango, which fills a caldera, just to the east. Britannica describes the conurbation as running continuously from Nueva San Salvador in the west to the shore of Lake Ilopango in the east, holding about one fourth of the national population. The census of 2024, which took 20 May as its census day, counted 1,563,371 people in the department of San Salvador out of a national total of 6,029,976, a share of 25.9%.

The ministry's volcanologists drew the exposure map from the census before that one. Of the roughly 2 million people they placed around the six monitored volcanoes, more than 1.5 million lived in the metropolitan area counted in 2007: the capital and 13 neighbouring municipalities near the San Salvador complex and around the Ilopango caldera. The same assessment, published by the Ministry of the Environment and Natural Resources in 2019, rated the San Salvador volcano at a very high risk level and the Ilopango caldera at a high one, after weighing the hazard against the population exposed to it.

The San Salvador volcano last erupted in 1917, a Strombolian eruption that built the cinder cone called Boqueroncito inside its crater, dropped ash on the southwest flank and sent out a lava flow. Seismometers have been deployed around it since 1984, eighteen years before the other monitored volcanoes received them in 2002, and by 2020 it carried three of the network's five permanent GPS stations.

Ilopango's eruptive history includes Plinian, phreatomagmatic and effusive phases, and in the fifth century AD it produced an eruption of strength 6 on the Volcanic Explosivity Index, with pyroclastic flows that devastated Maya cities. A 2019 study of its Tierra Blanca Joven eruption is titled as an account of "the major Holocene event of Central America". Its most recent eruption, in 1879 and 1880, was smaller and built the dacite dome of Islas Quemadas.

The ash also decides what archaeology can find. Joya de Cerén, a farming community buried by an eruption of the Laguna Caldera volcano around AD 600, which UNESCO compares with Pompeii and Herculaneum and whose remains survive in exceptional condition. El Salvador: history begins there.

How the Cocos Plate feeds the volcanic chain

The volcanic chain crosses the country from west to east, parallel to the coast. Off the shore the Cocos Plate, carrying the floor of the Pacific northeast, is forced down beneath the Caribbean Plate into the Middle America Trench. The descending rock melts, and the magma climbs through fractures in the overlying plate to the surface, which is also why earthquakes are frequent near the coast. Earthquakes in the far north come from a second source, the fault along the Motagua valley in Guatemala where the North American Plate grinds against the Caribbean.

The Global Volcanism Program's list of 2020 gives El Salvador 20 volcanoes with activity in the Holocene, and they are several different kinds of object. Most are stratovolcanoes, from Chingo in the west to San Miguel in the east. Coatepeque and Ilopango are calderas; San Diego, Cerro Cinotepeque and Apastepeque are volcanic fields; Cerro Singuil is a pyroclastic cone; and Laguna Aramuaca is a maar. For fifteen of the twenty the date of the last eruption is unknown.

Six are classed as active, because they have erupted within the past 500 years or are venting fumaroles now, and they are the six the observatory monitors.

The heights are the ministry's; Wikipedia gives Santa Ana as 2,384 metres in one article and 2,365 in another, and Britannica puts San Salvador at 1,960. For San Miguel the Global Volcanism Program's own table records an eruption in 2020, after the 2013 episode the ministry describes.

What the six have done within living memory

Izalco is the youngest volcano in the country, a cone that began to build in the eighteenth century and has erupted at least 54 times since 1770. From the early nineteenth century to the middle of the 1950s it erupted with a regularity that earned it the name "Lighthouse of the Pacific", its flares visible far out at sea. It last erupted in 1966.

Santa Ana is given to frequent phreatomagmatic activity. On 5 October 2005 it threw ballistic fragments up to 2.5 kilometres from the crater and emitted 1.5 million cubic metres of ash, and lahars after the eruption reached the shore of Lake Coatepeque. Wikipedia dates it to 1 October and records two deaths. San Miguel, in the east, erupts in the Strombolian style. Its episode of 29 December 2013 raised a column 7.6 kilometres high and produced 850,000 cubic metres of ash.

The same heat is put to work. Geothermal plants supplied 27.3% of the electricity injected into the grid in January 2021, 119.07 GWh. The state's Bitcoin Office reported in May 2024 that the government had mined nearly 474 bitcoin since September 2021 with geothermal power drawn from the Tecapa volcano.

How disasters built the state's observatory

San Salvador was destroyed by earthquakes in 1756 and again in 1854, and suffered heavy damage in 1919, 1982 and 1986. The 1986 earthquake, of magnitude 5.7, killed 1,500 people. On 13 January 2001 a magnitude 7.7 earthquake set off a landslide that killed more than 800 people, and a second earthquake on 13 February 2001 killed 255 and damaged about 20% of the country's housing. Together they left nearly 2,000 people dead or missing and about 1.5 million without housing.

The institutions that watch the ground were built in steps, and the largest step followed that disaster. A National Geological Service was set up in 1955 inside the Ministry of Public Works, directed by the German geologist Helmut Meyer-Abich, who worked on its seismic instruments. Its successor, the Centre for Geotechnical Research, produced the national geological map with a German mission from 1967 to 1971. In 2001, in direct response to the earthquakes of January and February, the government created the National Service for Territorial Studies, which took in the old centre's scientists and the weather and hydrological services. In 2011 an integrated monitoring centre inside the ministry began watching volcanoes, earthquakes, landslides, rivers and weather around the clock.

In 2020 the volcano team numbered 14 people, three of them volcanologists, working two shifts of 10 and 14 hours every day of the year. Webcams on San Miguel and Santa Ana have streamed since 2006. Official hazard maps exist for four of the six, Santa Ana, San Salvador, San Vicente and San Miguel, and an early warning system was set up at San Miguel in 2016 after its eruption.

Every monitored volcano also has a network of trained local observers, residents who report changes in activity or in the shape of the cone. The ministry's volcanologists call contact with them the most practical way of reaching the people at risk.

What lies north and south of the volcanic chain

The country stretches 270 kilometres from west-northwest to east-southeast and 142 kilometres from north to south. Two parallel mountain ranges cross it with a central plateau between them and a narrow plain along the Pacific, and together the ranges and the plateau, called the interior highlands, cover 85% of the land. The Pacific lowlands are the rest.

The northern range runs unbroken along the border with Honduras. Britannica gives its average elevation as 1,500 to 1,800 metres, formed from ancient and heavily eroded volcanic structures, with limited outcrops of limestone in the far northwest that belong to the older, non-volcanic geology of Honduras. The highest ground in the country is here: Cerro El Pital, on the Honduran border in the department of Chalatenango, at 2,730 metres. The ministry's own climate page gives El Pital as 2,700 metres. Clearance and overworked soils have left much of the once forested north semibarren. The 2024 census found 185,930 people in all of Chalatenango.

Between that range and the volcanoes, Britannica describes a broad interior plain drained by the Lempa at 400 to 610 metres, broken by old dormant volcanic structures and held back by poor drainage and acid soils, which Britannica calls a less attractive environment for settlement. The central plateau proper sits among the volcanoes. Wikipedia describes a plain about 50 kilometres wide at an average of 600 metres, covering 25% of the land and carrying the country's largest cities. Britannica places the basins between the cones at 1,000 to 1,500 metres. Britannica puts more than three fourths of the population in the intermontane basins of the central highlands, on soils formed from ash, lava and alluvium that have been farmed for centuries. Santa Ana, Ahuachapán, San Salvador, San Vicente and San Miguel, the principal Spanish colonial settlements, all stand in these basins.

To the south the plain along the Pacific is between one and thirty-two kilometres wide, at 30 to 150 metres, and at its widest in the east beside the Gulf of Fonseca. Near La Libertad it disappears, and the slopes of the volcanoes come straight down to the sea. Since 1945 its alluvial soils have been turned over to cotton and cattle. The coast is 307 kilometres long.

Where the Lempa carries half the country's water

El Salvador has more than 300 rivers, and apart from one they are generally short, draining the Pacific lowlands or running from the plateau through gaps in the volcanic range to the sea. The exception is the Lempa. It rises in Guatemala and flows east for 130 kilometres across the interior plain, forms part of the border with Honduras, then turns sharply south and runs 105 kilometres through the volcanic range and across the coastal plain to the sea. With its tributaries it drains about half the country. Boats could travel several miles up it until two large hydroelectric installations were built on its middle reaches in the mid-1950s, and the Cerrón Grande dam on the Lempa holds a reservoir of 135 square kilometres in the north. Hydroelectric plants supplied 28.5% of the electricity injected into the grid in January 2021. The east drains through the Río Grande de San Miguel.

The natural lakes are mostly volcanic, sitting in craters under high, steep banks, and their sizes depend on who measured them. Wikipedia gives Lake Ilopango 70 square kilometres and Lake Coatepeque 26; Britannica gives them 100 and 39. Wikipedia calls Lake Güija, on the Guatemalan border, the largest natural lake at 44 square kilometres, a figure smaller than its own one for Ilopango. Water covers 320 square kilometres within the country's borders in all.

The Lempa is also where floods do most damage. Hurricane Mitch, which formed in the Atlantic and crossed Central America in late October 1998, flooded roughly 650 square kilometres, and the government counted 374 people dead or missing and about 55,900 left homeless. The worst-hit ground was the low coastal plain, above all the floodplains of the Lempa and the San Miguel. Three major bridges over the Lempa were swept away, which restricted access to the eastern third of the country.

Why the rain arrives from one ocean

The territory lies wholly on the western side of the isthmus and has no Caribbean coast, and the climate follows from that. The rainy season, which Salvadorans call invierno, winter, runs from May to October and brings almost all of the year's rain, generally from low pressure over the Pacific and usually in heavy afternoon thunderstorms. Britannica records the heavy rains of the season as the temporales. From November to April the northeast trade winds take over. The air they carry has crossed the Caribbean and dropped most of its moisture on the mountains of Honduras, and by the time it arrives it is dry, hot and hazy. That season is verano, summer. The national weather service adds the occasional gusty nortes, which bring cool air from the polar regions of North America, much warmed on its way across the Gulf of Mexico.

Temperature varies more with height than with the season. The service divides the country into three thermal zones by elevation.

The lowest, from sea level to 800 metres, averages 27 °C on the coastal plains and 28 °C on the inland plains at the bottom, falling to 22 °C at the top. Between 800 and 1,200 metres it falls from 22 to 20 °C, and the valleys and hollows above 1,800 metres average 16 to 10 °C. In the mountains minimum temperatures sometimes approach freezing. San Salvador averages 23 °C over the year.

Britannica gives about 1,700 millimetres a year on the Pacific lowlands, 1,800 to 2,500 millimetres on the mountain ranges between 600 and 1,060 metres, and 1,100 to 1,500 millimetres in the deeper valleys and the plateau-like ground around them. Wikipedia gives totals of up to 2,000 millimetres on south-facing mountain slopes.

Hurricanes form in the Pacific from time to time and seldom reach the country; Hurricane Emily in 1973 and Mitch in 1998, which came from the Atlantic, are the recorded exceptions. Heavy rainstorms and severe droughts both occur, and El Niño and La Niña can make either more extreme. In the summer of 2001 drought destroyed 80% of the country's crops and brought famine to the countryside, and on 4 October 2005, in the same week as the Santa Ana eruption, heavy rains set off floods and landslides that killed at least 50 people.

Who owns the land set aside for protection

The answer to how much of El Salvador is protected depends on what counts. In its sixth national report to the Convention on Biological Diversity, the Ministry of the Environment stated that 24.83% of the territory was under some mechanism of protection or conservation. A study for the Friedrich Ebert Foundation, reported by Diario El Mundo in June 2024, put the share declared as Protected Natural Areas at 0.61%. The difference is legal. Conservation areas, biosphere reserves, Ramsar sites and biological corridors are almost entirely privately held, and the study argued that they cannot be counted as protected territory, since only the Protected Natural Areas carry a legally backed declaration. The ministry had declared 197 such areas by June 2023, and 80% of them are private.

Cerro El Pital shows how the process works. It was declared protected in 2014, but the study found that 70% of its owners were from Las Pilas and Los Planes, and five of the twelve registered owners asked for their land to be removed from the designation, saying the ministry had not properly informed them what it implied and that promised support had never arrived.

Pine and oak forest and cloud forest cover the high mountains, tropical dry forest many lower slopes, and the izote is the national flower. Four of the six sea turtle species that nest on Central American shores live on the Salvadoran coast: the leatherback, the hawksbill, the green turtle and the olive ridley. El Imposible national park is managed by a non-governmental organisation, SalvaNatura, under an agreement with the environmental authorities.

How much forest exists depends on definitions too. Global Forest Watch counts 988,821 hectares of tree cover above 30% density in 2000, about 47% of the country's area, and a cumulative loss of 85,433 hectares from 2001 to 2024, about 8.6% of that baseline. The forest reference level the country submitted under the United Nations climate convention in 2021 uses a minimum of half a hectare, four metres of height and 30% canopy cover, and it counts agroforestry and shade coffee plantations as forest.

The constitution makes the environment a duty of the state. Article 117 obliges it to protect natural resources and bans the import of nuclear residues and toxic waste. Metal mining was prohibited in 2017 after sustained opposition, and in December 2024 the Legislative Assembly lifted the ban and allowed mining to resume under conditions. In a survey by the Central American University, 67% of respondents said the country already faced a water crisis and was unsuited to metal mining.

Where El Salvador's borders and waters end

The two published figures for the land border do not agree. Wikipedia's article on the country gives 546 kilometres, 203 with Guatemala and 343 with Honduras; its geography article gives 590, 199 with Guatemala and 391 with Honduras. The constitution fixes the lines by treaty. Article 84 sets the western border by the treaty signed with Guatemala on 9 April 1938, and the northern and part of the eastern border by the General Peace Treaty signed with Honduras in Lima on 30 October 1980, with the sections still pending to be settled under that treaty or by other peaceful means.

Under the 1980 treaty the two countries took the gulf and five sections of the land boundary to the International Court of Justice. In 1992 the court awarded most of the disputed land to Honduras, around 374.5 square kilometres; Britannica gives Honduras two thirds of the land in the gulf and free passage to the Pacific. Of the islands, the court found Honduras sovereign over El Tigre and El Salvador over Meanguera and Meanguerita. El Salvador accepted the ruling in 1999, and the countries' differences over the gulf went on: in March 2013 Honduras and El Salvador exchanged letters threatening military action. This catalogue records the disagreement and takes no position on it.

The easternmost point of the country is the island of Meanguera del Golfo. The constitution describes the territory as irreducible, includes the islands named by the Central American Court of Justice on 9 March 1917, treats the Gulf of Fonseca as a historic bay with the character of an enclosed sea held in community, and claims sovereignty over the sea, the subsoil and the seabed to 200 nautical miles from the low-tide line. Its exclusive economic zone is given as 90,962 square kilometres, more than four times the land.