Satonda Island
   HOME

TheInfoList



OR:

Satonda is a volcanic island off the northern coast of Sumbawa, in
West Nusa Tenggara West Nusa Tenggara ( – NTB) is a provinces of Indonesia, province of Indonesia. It comprises the western portion of the Lesser Sunda Islands, with the exception of Bali which is its own province. The area of this province is which consists of ...
province of
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
. The lake on the island has helped to gain some insight in the formation of organisms.


Location

Satonda is situated north of
Sumbawa island Sumbawa, is an Indonesian island, located in the middle of the Lesser Sunda Islands chain, with Lombok to the west, Flores to the east, and Sumba further to the southeast. Along with Lombok, it forms the province of West Nusa Tenggara, but the ...
and west of Mojo island, in the
Flores Sea The Flores Sea covers of water in Indonesia. The sea is bounded on the north by the island of Celebes and on the south by Sunda Islands, the Sunda Islands of Flores and Sumbawa. Geography The seas that border the Flores Sea are the Bali Sea ...
, 3 km east of Sanggar Strait that separates both these islands, and less than 30 km north-west of the Tambora volcano Administratively, it is in Pekat District, in
Dompu Regency Dompu Regency (; ) is a regency of the Indonesian Province of West Nusa Tenggara. It is located on the island of Sumbawa and the capital is Dompu. It is bordered to the north and to the east by two non-contiguous parts of Bima Regency, and to t ...
,


Description

The island is about 3 x 2 km in size, with an elongated axis oriented NW-SE. The caldera is about 2 x 2 km and its walls rise to about 300 m. A lake occupies the caldera. At one point on the south side, the height of the crater rim is reduced to 13 m altitude and its width is reduced to about 30 m. Satonda Island has a vast natural coral reef in the surrounding waters and was designated a Marine Nature Park (TWAL) in 1999 by the Ministry of Forestry of Indonesia. The island is proposed to be part of ''Moyo Satonda National Park'' along with neighbouring
Moyo Island Moyo (older spelling Mojo) is an island off the north coast of Sumbawa Island, in Sumbawa Regency, West Nusa Tenggara province, Indonesia. Description, administrative divisions It has an area of 349 km2 and is about 8° south of the equator. ...
.


Satonda volcano

The volcano rises from a depth of about 1,000 m underwater, with the steep slope typical of
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...
cones. Its caldera is about 2 x 2 km large and the caldera walls rise up to 300 m above sea level. The eastern wall is very steep and has no vegetation. The
Sangeang Api Sangeang Api (Gunung Api or Gunung Sangeang) is an active complex volcano on the island of in Indonesia. It consists of two volcanic cones, Doro Api and Doro Mantoi. Sangeang Api is one of the most active volcanoes in the Lesser Sunda Islands. ...
(island of Sangeang) and Satonda are eruption centers associated to the Tambora volcano — and therefore to the phenomenal 10–15 April
1815 eruption of Mount Tambora In April 1815, Mount Tambora, a volcano on the island of Sumbawa in present-day Indonesia (then part of the Dutch East Indies), erupted in what is now considered the most powerful volcanic eruption in recorded human history. This eruption, with ...
which ejected 50km3 of rock (150 km3 of
pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...
and pyroclastics) and affected a large part of the Earth. Signs of erosion such as the marine terraces to the south of the island, and steep gullies (deep erosional ravines in the tuff ring), indicate that the volcano has been inactive since several thousand years, and maybe tens of thousands of years. The volcano may have been formed when the sea level was lower, during the last ice age


The lake

There is a
soda lake A soda lake or alkaline lake is a lake on the strongly base (chemistry), basic side of neutrality, typically with a pH, pH value between 9 and 12. They are characterized by high concentrations of carbonate salts, typically sodium carbonate (and ...
in the middle of the island, occupying two intersecting craters 39 and 69 meters deep as determined by echo-sounding. The southern crater is 950 m in diameter and the northern one is 400 m in diameter; at the bottom they are separated by a 10 m high ridge. The lake is surrounded by sandy beaches. At 13 sites around the lake, large calcareous reefs extrude from rocky points; they are submerged for at least 23 m, are 1 to 2 m thick with very steep walls, and their tip emerge by about 50 cm at the end of the dry season. They are made of brittle, cavernous limestone composed of
aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...
and low-Mg-
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
, partly
silicified In geology, silicification is a process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO2). Silica is a naturally existing and abundant com ...
. Their structure alternates between layers of ''in vivo'' calcifying
Pleurocapsales The Pleurocapsales are an order of coccooid cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their blu ...
cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...
and of
red algae Red algae, or Rhodophyta (, ; ), make up one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest Phylum, phyla of algae, containing over 7,000 recognized species within over 900 Genus, genera amidst ongoing taxon ...
('' Peyssonnelia'' sp., '' Lithoporella'' sp.), often separated by accumulations of gastropod fecal pellets settled in cyanobacterial
micrite Micrite is a limestone constituent formed of calcareous particles ranging in diameter up to four μm formed by the recrystallization of lime mud. Flügel, Erik, ''Microfacies of Carbonate Rocks: Analysis, Interpretation and Application,'' Springe ...
— although the red algae are present only in the first 1 cm of the reefs. The pellets are produced by the '' Cerithium'' species; these and the gastropods' shells contribute significantly to the mass of the reef. The fauna in the lake is extremely poor in species; contrary to what one could expect, hardly any colonization seems to issue from the nearby reef only 100 m away and boasting a thriving diversity of tropical marine reef species. In 1990 the following species were noted (some of which may be endemic): one species of thin-shelled cerithiid gastropod; one species of monaxonid
demosponge Demosponges or common sponges are sponges of the class Demospongiae (from + ), the most diverse group in the phylum Porifera which include greater than 90% of all extant sponges with nearly 8,800 species A species () is often de ...
; one species of amphipod crustacean; one species of small fish; one species of
hydrozoa Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomy (biology), taxonomic class (biology), class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline wat ...
; one species of infaunal oligochaet; and three species of green algae. There were also, in reef and sediment samples, subfossil shells of two bivalve species (''
Lioconcha ''Lioconcha'' is a genus of molluscs in the family Veneridae.Van der Meij, S.E.T., Moolenbeek, R.G., & Dekker, H. (2010). "The ''Lioconcha castrensis'' species group (Bivalvia: Veneridae) with the description of two new species." ''Molluscan Rese ...
'' sp.?, ''
Pinctada ''Pinctada'' is a genus of saltwater oysters, marine bivalve mollusks in the family Pteriidae. These pearl oysters have a strong inner shell layer composed of nacre, also known as "mother of pearl". Pearl oysters are not closely related to ...
'' sp.?); three gastropod species ('' Cerithium'' sp., common; '' Ocenebra'' sp., seldom; and '' Neritina'' sp., rare); and dense aggregates of ''
serpulid The Serpulidae are a family of sessile, tube-building annelid worms in the class Polychaeta. The members of this family differ from other sabellid tube worms in that they have a specialized operculum that blocks the entrance of their tubes wh ...
'' tubes. A population of monaxonid sponges ('' Suberites'' sp.) colonizes the reefs surfaces, intertwining with the green algae; and a dense population of
Oligochaeta Oligochaeta () is a subclass of soft-bodied animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadril ...
(worms) lives in the black sandy mud on the lakeshore. The lake has been extensively researched by biogeologists Stephan Kempe and Josef Kazmierczak since 1984.
Radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotop ...
indicates that the lake was invaded by sea water 4,000 years ago, maybe because of a collapse in part of the crater rim; the water was quickly alkalised, and the reefs started growing soon after.
Its water has three layers. The upper one is 22.8 m thick, it is oxygenated; compared to seawater, it is less saline but more
alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...
, has a higher pH, and lower concentrations of Ca and Mg.
The 22.8 m deep
chemocline A chemocline is a type of cline, a layer of fluid with different properties, characterized by a strong, vertical chemistry gradient within a body of water. In bodies of water where chemoclines occur, the cline separates the upper and lower layers, ...
is marked by a sharp decrease of the pH, which indicates an increase in pCO2 (partial pressure of carbon dioxide): from 340 ppmv (part per million by volume) at the surface, it rises to 240,000 ppmv at the bottom of the lake.
The two other layers underneath are
anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...
and more saline than seawater. Alkalinity increases considerably with depth: it goes from 3.4 meq/kg near the surface, to nearly 50 meq at the bottom of the lake. On the other hand, Ca concentration hardly increases. suggest that organic matter falling into the lake is progressively respired at depth, releasing isotopically light CO2. The increase in pCO2 causes weathering of the silicates at the bottom of the lake, as well as weathering of the 80 cm of ashes received during the eruption of the Tambora in 1815. The weathering of silicates increases the alkalinity. The water degases at the surface, which increases the pH and, because of the high alkalinity, brings a supersaturation of carbonate minerals. In surface waters, saturation index (SI) for
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
— which is a
calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
polymorph, CaCo3 — is above 0.8 and that for dolomite is above 2.8; both values decrease rapidly with depth, and undersaturation is reached below the chemocline.
In the upper layer, the supersaturation allows microlithes to extract CaCo3, which explains the low amount of Ca; it seems that no enzymes are involved in this extraction. The amount of Ca is still significantly higher than that in sea water. As a succinct summary, it can be said that the high level of alkalinity causes a high supersaturation of calcium carbonate minerals and the formation of modern analogues of Precambrian microbialitic
stromatolite Stromatolites ( ) or stromatoliths () are layered Sedimentary rock, sedimentary formation of rocks, formations (microbialite) that are created mainly by Photosynthesis, photosynthetic microorganisms such as cyanobacteria, sulfate-reducing micr ...
s along the fringes of the lake. This confers to the lake a significant scientific importance: the
Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...
somme 6 M years ago saw the extinction of cyanobacterial stromatolithes along with 3/4 of all plant and animal species. Riding (1982) had suggested that their disappearance was due to a modification of the Mg/Ca ratio; suggested instead that it was more likely due to changes in the saturation index of calcite (both ideas are not mutually exclusive, because the solubility of calcite increases when its magnesium content rises — see page "
Marine biogenic calcification Marine biogenic calcification is the production of calcium carbonate by organisms in the global ocean. Marine biogenic calcification is the biologically mediated process by which marine organisms produce and deposit calcium carbonate minerals to ...
"). Thus the lake has been closely linked with the "Soda Ocean Hypothesis"; Kempe & Kazmierczak have qualified lake Satonda as "a recreated model of late Precambrian ocean chemistry" — that is, the "
soda lake A soda lake or alkaline lake is a lake on the strongly base (chemistry), basic side of neutrality, typically with a pH, pH value between 9 and 12. They are characterized by high concentrations of carbonate salts, typically sodium carbonate (and ...
" environment that prepared the great explosion of life during the
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
.


Notes


References


Bibliography

* * * * * * * * * * {{Portal, Indonesia Islands of West Nusa Tenggara Lesser Sunda Islands Tourism in Indonesia