The geography of Aruba, located at the juncture of the South American and Caribbean tectonic plates, has been shaped by a complex interplay of geological processes. From its flat expanses to its rugged coastlines, Aruba's geography and geology reveal the island's geographical diversity and its underlying geological formations, offering a comprehensive understanding of Aruba's terrain and environmental dynamics of this Caribbean destination.
Geography Aruba (the westernmost island among the ABC Islands and of the Leeward Antilles) is situated in a unique geological location, right at the boundary between the South American and Caribbean tectonic plates. It is located north of the Venezuela coast and northwest of Curaçao. Aruba covers a total area of and a coast line of . This region is characterized by a complex fault system where the Caribbean Plate moves westward in relation to South America. Aruba is the westernmost island in the Aruba-La Blanquilla Chain, a series of small islands and atolls located along the Venezuelan continental border.
Aruba, as well as the rest of the ABC islands and also Trinidad and Tobago, lies on the continental shelf of South America, and is thus geologically considered to lie entirely in South America.
Landscape The geography of Aruba is characterized by a relatively flat to gently rolling terrain with some low hills. The highest point on the island is Jamanota, reaching almost in elevation. There are three distinct types of landscapes on the island.
In the western part, features a gently sloping plain with shallow dry valleys. This area is flanked by a zone of horizontal bedded to slightly seaward-dipping limestone rocks on its western side. Moving towards the central part of the island, the terrain becomes more rugged. This region developed in the outcrop area of the metamorphosed volcanic rocks of the Aruba Lava Formation (ALF), and it features east-to-west running valleys controlled by faults. The ALF cover an area of approximately . The southeastern part of Aruba is predominantly defined by Neogene and younger limestone formations. Along the eastern coast, near Boca Grandi and Seroe Colorado, well-developed Quaternary terraces can be observed. Forereef deposits line the south and southwestern coast between Ceru Colorado and the urban center of Oranjestad.
The arid landscape in Aruba is not solely a product of its climate but is also a consequence of extensive deforestation and exploitation during the Spanish colonization of the island. Consequently, certain crops, such as aloe vera, thrive in this environment, due to the high calcium-rich soil known as liming. As of 2022, Aruba only has 2.3% of forest-covered land area and only 0.5% of protected natural area. In Aruba forest cover is around 2% of the total land area, equivalent to 420 hectares (ha) of forest in 2020, which was unchanged from 1990. In 2020, naturally regenerating forest covered 420 hectares (ha) and planted forest covered 0 hectares (ha). Of the naturally regenerating forest 0% was reported to be primary forest (consisting of native tree species with no clearly visible indications of human activity) and around 0% of the forest area was found within protected areas.
Elevations Aruba is predominantly characterized by its flat terrain. However, there are notable exceptions that add diversity to its landscape. Two well-known rock formations, the Ayo and Casibari Rock Formations.
In contrast, the northern coast of Aruba features a more hilly topography, particularly within the Arikok National Park. The island's highest point, Jamanota, stands at a modest elevation of above sea level, while Arikok itself reaches . Another prominent landmark, Hooiberg, rises to . Despite not being the island's highest peak, Hooiberg appears as such due to its location in the flat surroundings. It is a recognizable feature that can be observed from nearly every point on the island.
Coastal form
In stark contrast to the southern shores, Aruba's northern sea is typically characterized by rough waters with a deep blue hue, rocky terrain and consists mostly of wave-cut coral limestone terraces interspersed with small sandy coves referred to as boca in Papiamento, which translates to "mouth" in English. The marine terraces of Aruba are most prominent on their windward, or northeast, coasts. In these areas, some of the terraces exhibit wide platforms and steep, angular backslopes. Conversely, on the leeward, or southwest, sides of the islands, the terraces tend to have narrower platforms and gentler backslopes. On occasion, particularly on the southwest side of Aruba, the backslopes are less distinct.
The distinctive appearance of the wave-cut terraces is influenced by the islands' location within the arid region along the southern Caribbean coastline. Limestone, known for its resistance to the effects of arid climate weathering, has contributed to the remarkable preservation of these terraces. Although a light layer of xerophytic vegetation lightly covers their surfaces, the terraces remain excellently preserved.
Aruba has a barrier reef, it generally lies about offshore and extends along the southwest coast between Punta Brabo and Oranjestad. It is composed of coral and is capped by a beach ridge of coral fragments in height. On the seaward side, the reef extends to a depth of at least .
Geological development
The oldest geological unit visible on Aruba is the ALF, which comprises volcanic and volcaniclastic rocks of basaltic composition, with a thickness exceeding . These rocks have undergone metamorphism due to the intrusion of the Aruba Batholith. The age of this formation is believed to be Turonian, supported by ammonite imprints found in conglomeratic mudstone.
The Aruba Batholith, which intruded the Aruba Lava Formation, primarily consists of hornblende tonalite. Pendants of quartz-norite to quartz-hornblende gabbro are present in the roof of the tonalite. Both the Aruba Lava Formation and the batholith are intersected by numerous dikes. The batholith's intrusion occurred around 85 to 90 million years ago, with subsequent reheating of the rocks between 73 and 67 Myr.
The limestone terraces are categorized based on their elevation, a feature commonly associated with slow uplifting active margins. The lower terrace, situated at an elevation of , has a range age of 30–129 thousand years (Kyr). In contrast, the middle terrace, located at , dates back up to 510 Kyr, indicating a slow (0.05 mm/yr) rate of tectonic uplift of Aruba.
Aruba was above sea level during the Oligocene epoch. However, Aruba later subsided beneath the sea level in the middle Miocene, as documented by the emergence of widespread elevated coastal limestone terraces. This geological history has left a distinct mark on Aruba's landscape and formation.
Biogeography
Non-native species
Goats
Introduced in the early 16th century, feral goats (Capra hircus) and donkeys pose a significant threat to Aruba's environments, causing both direct and indirect harm due to excessive grazing. This often leads to ecosystem deterioration and a decline in biodiversity. Despite their impact, these animals remain a local food source, with goat stew and soup being popular dishes in the region. Arikok, spanning 20% of the country, is home to a substantial goat population. Recent research estimates the goat population at approximately 1,465 individuals by counting fresh pellets.
Lionfish The lionfish, originally from the Indo-Pacific, were introduced to the Atlantic Ocean in the mid-1980s. Their population has since grown significantly because they lack natural predators in their new environment. This unchecked growth has led to a decline in fish and crustacean populations, and even the health of coral reefs is suffering as herbivorous fish vanish. NOAA researchers confirm that invasive lionfish populations will keep increasing and can't be eradicated using conventional methods.
Aruba LionFish Initiative (ALFI), a group of divers that regularly hunt invasive species, have taken the initiative to reduce the lionfish population in coastal areas by hunting them for food and crafting jewelry from their fins.
Boa constrictor In 1999, the initial boa constrictor was discovered in Aruba. Despite attempts to control their growth, a population covering the entire island had taken hold by 2005. Being an invasive species, their adaptable diet can potentially endanger many native populations. A 2021 study examined the stomach contents of more than 500 captured Aruban boas. The findings revealed over 400 distinct prey types, with an almost equal distribution among mammals, lizards, and birds. Remarkably, aside from the seven known bat species in Aruba, nearly every other type of vertebrate was found in the stomach contents analyzed.Reinert, H. K., Leto, A. E., Tumaliuan, J. A., Jackrel, S., Lutterschmidt, W. I., Bushar, L. M., & Odum, R. A. (2021). A long-term dietary assessment of invasive Boa constrictor on Aruba. Herpetological Conservation and Biology, 16(1), 211-224.
Cane toad The Cane toad, also called Sapo locally, is an invasive species with a detrimental impact on Aruba's fauna, such as the Dori (Pleurodema brachyops). However, the Aruban Cat-eyed Snake or Santanero (Leptodeira bakeri) preys on these toads and is considered a natural "pest control". Toads favor damp environments, including (irrigated) gardens of residential homes and tourist accommodations, such as hotels and resorts. However, toads are true survivors and can easily adapt to drier conditions, as found in the arid climate of the Caribbean islands.
Anoles and geckos In 2019, three new non-native reptiles have been discovered on Aruba, including Anolis gingivinus, Anolis cristatellus, Hemidactylus frenatus. Anole and gecko species are often unintentionally introduced to Caribbean islands through the live plant trade, but can also be intentionally introduced as pets. Similar to many non-native lizards in the Caribbean, these species often inhabit human-altered environments (anthropogenic habitats), and their impacts on Aruba's native species is not yet fully understood. Aruba has a recorded history of 10 previous introduction of non-native reptiles species, including two anoles, Anolis sagrei and A. porcatus, and four geckos, Gonatodes albogularis, G. antilensis, G. vittatus, and Hemidactylus mabouia.
Climatology
Located within the tropics, Aruba features a hot semi-arid climate (Köppen BSh) characterized by consistently warm temperatures throughout the year. There have been lasting environmental challenges linked to climate and nature. Sea water temperatures, for example, have gradually risen by at least since the 1950s.
Southern Oscillation impact The rainy season typically occurs between September and January. However, it exhibits significant variability due to the strong influence of the Southern Oscillation.Dewar, Robert E. and Wallis, James R; ‘Geographical patterning of interannual rainfall variability in the tropics and near tropics: An L-moments approach’; in Journal of Climate, 12; pp. 3457-3466 During strong El Niño years like 1911/1912, 1930/1931, 1982/1983 and 1997/1998 annual (fiscal year) rainfall can plummet to as little as . In contrast, during La Niña years like 1933/1934, 1970/1971, 1988/1989, 1999/2000 or 2010/2011, rainfall can soar to as much as . The highest monthly totals during these La Niña events can reach between .
Conservation geography The origins of over-tourism can be traced back to the 1970s and 1980s when people first expressed concerns about the possible negative effects on society and the environment due to uncontrolled tourism growth. These concerns also included the long-term economic consequences.