The Seven Lakes of San Pablo (Filipino : Pitong Lawa ng San Pablo) are seven volcanic crater lakes scattered around the City of San Pablo, in the province of Laguna, Philippines.
The canonical list of seven lakes are:
The lakes are maars or low-profile volcanic craters located in the San Pablo Volcanic Field. They are among the 200 small monogenetic volcanoes found along the Macolod Corridor, a rift zone between Mount Makiling and Mount Banahaw, which is part of the larger Southwestern Luzon Volcanic Field. [2] These craters are formed by phreatomagmatic eruptions, an eruption where ground water comes in contact with hot magma pushing up near the Earth's surface. [2]
In a recent rocks and sediment analysis or petrographic study on the lakes and adjoining rivers in San Pablo, sulfate concentrations were considerably higher than the naturally occurring sulfates from volcanism. Samples were taken from other areas underlain with similar volcanic rocks from the old eruptions (e.g. Taal volcano) like Indang, in the province of Cavite and the La Mesa Watershed, the water supply reservoir for Metropolitan Manila. The analyses indicated that the elevated level of sulfates were not related to volcanism but anthropogenic or man-made, and among the causes are sewage, fertilizers, herbicides, pesticides etc. [2]
In 2005, the Rotary Club of San Pablo City held a ceremony that officially opened the hiking trails that connect the seven lakes of the city. The Rotarians were aiming for economic, environmental and health benefits of the trails to the community. [3]
The lakes are threatened by human intervention and exploitation, most especially Lake Sampaloc, which is located right in the center of San Pablo City. Several illegal settlements, illegal fish pens, commercial and business infrastructures on the shores have proliferated on some of the lakes causing increased pollution. [4] [5] [6] Overuse of commercial fish feeds have resulted in high nitrogen levels and low dissolved oxygen that has led to fish kills in the early and late 1990s. In January 2004, fish kills were observed in six of the seven lakes. [7] Various ecological conservation efforts by both government and non-government organizations, like the Friends of the Seven Lakes Foundation, had been implemented in recent years. One of these is the demolition of human-made structures along the lakes' shoreline. [8]
A caldera is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the structural integrity of such a chamber, greatly diminishing its capacity to support its own roof, and any substrate or rock resting above. The ground surface then collapses into the emptied or partially emptied magma chamber, leaving a large depression at the surface. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. Compared to the thousands of volcanic eruptions that occur over the course of a century, the formation of a caldera is a rare event, occurring only a few times within a given window of 100 years. Only eight caldera-forming collapses are known to have occurred between 1911 and 2018, with a caldera collapse at Kīlauea, Hawaii in 2018. Volcanoes that have formed a caldera are sometimes described as "caldera volcanoes".
San Pablo, officially the City of San Pablo, is a 1st class component city in the province of Laguna, Philippines. According to the 2020 census, it has a population of 285,348 people.
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption. A maar characteristically fills with water to form a relatively shallow crater lake, which may also be called a maar.
Masaya is a caldera located in Masaya, Nicaragua, 20 km (12 mi) south of the capital Managua. It is Nicaragua's first and largest national park, and one of 78 protected areas of Nicaragua. The complex volcano is composed of a nested set of calderas and craters, the largest of which is Las Sierras shield volcano and caldera. Within this caldera lies a sub-vent, which is Masaya Volcano sensu stricto. The vent is a shield type composed of basaltic lavas and tephras and includes a summit crater. This hosts Masaya caldera, formed 2,500 years ago by an 8 km3 (1.9 cu mi) basaltic ignimbrite eruption. Inside this caldera a new basaltic complex has grown from eruptions mainly on a semi-circular set of vents that include the Masaya and Nindiri cones. The latter host the pit craters of Masaya, Santiago, Nindiri and San Pedro. Observations in the walls of the pit craters indicate that there have been several episodes of cone and pit crater formation.
An active volcano is a volcano that has erupted during the Holocene, is currently erupting, or has the potential to erupt in the future. A volcano that is not currently erupting but could erupt in the future is known as a dormant volcano. Volcanoes that will not erupt again are known as extinct volcanoes.
Mount Banahaw is an active complex volcano on Luzon in the Philippines. The three-peaked volcano is located at the boundary of Laguna and Quezon provinces. It is the highest mountain in both provinces and Calabarzon region, dominating the landscape for miles around.
Antofagasta de la Sierra is a volcanic field in Argentina. The main type of volcanic edifice in the area are scoria cones, it is formed by the La Laguna, Jote and Alumbrera volcanoes. The first and last of these form a sub-group which is better researched. Various dating methods have yielded ages from several million to several hundred thousand years ago, but some vents appear to be of Holocene age.
Viedma is a subglacial volcano whose existence is questionable. It is supposedly located below the ice of the Southern Patagonian Ice Field, an area disputed between Argentina and Chile. The 1988 eruption deposited ash and pumice on the ice field and produced a mudflow that reached Viedma Lake. The exact position of the edifice is unclear, both owing to the ice cover and because the candidate position, the "Viedma Nunatak", does not clearly appear to be of volcanic nature.
Taal Lake, formerly known as Bombón Lake, is a fresh water caldera lake in the province of Batangas, on the island of Luzon in the Philippines. The lake fills Taal Volcano, a large volcanic caldera formed by very large eruptions between 500,000 and 100,000 years ago.
The Alvarez hypothesis posits that the mass extinction of the non-avian dinosaurs and many other living things during the Cretaceous–Paleogene extinction event was caused by the impact of a large asteroid on the Earth. Prior to 2013, it was commonly cited as having happened about 65 million years ago, but Renne and colleagues (2013) gave an updated value of 66 million years. Evidence indicates that the asteroid fell in the Yucatán Peninsula, at Chicxulub, Mexico. The hypothesis is named after the father-and-son team of scientists Luis and Walter Alvarez, who first suggested it in 1980. Shortly afterwards, and independently, the same was suggested by Dutch paleontologist Jan Smit.
Cuicocha is a 3 km (2 mi) wide caldera and crater lake at the foot of Cotacachi Volcano in the Cordillera Occidental of the Ecuadorian Andes.
Reclus, also written as Reclús, is a cinder cone and stratovolcano located in the Southern Patagonian Ice Field, Chile. Part of the Austral Volcanic Zone of the Andes, its summit rises 1,000 metres (3,300 ft) above sea level and is capped by a crater about 1 kilometre (0.62 mi) wide. Close to the volcano lies the Amalia Glacier, which is actively eroding Reclus.
Lake Sampaloc is a volcanic crater lake in Laguna on the island of Luzon. It is the largest of the Seven Lakes of San Pablo. Nearly half of the lake's depth has a shallow depression at the bottom, indicating its volcanic origin. The lake is behind San Pablo city hall and is dotted with fishpens and small cottages built on stilts.
Lake Calibato is one of the seven crater lakes collectively called Pitong Lawa or Seven Lakes of San Pablo in Laguna province in the Philippines. The lake is situated in Brgy. Sto. Angel in San Pablo City. Calibato has an area of 42 hectares and maximum depth of 135 metres (443 ft). Calibato's maximum water capacity is approximately 29,600 cubic metres (1,050,000 cu ft). Its supplies the city and nearby towns with abundant fish and aquatic plants. The lake is the deepest recorded lake among the seven-lake system; no recorded depths are available for Muhikap.
The Laguna Volcanic Field, also known as the San Pablo Volcanic Field, is an active volcanic field in the Philippines, located between Laguna de Bay, Mount Banahaw volcano complex and Mount Malepunyo range. It is part of the larger Southwestern Luzon Volcanic Field (SWLVF). From Manila, it is about 50 kilometres (31 mi) southeast to Mount Makiling, its most prominent volcanic feature.
Lake Tikub is a nearly circular crater lake located in the province of Quezon, in the Philippines. The circumference of the lake is elevated and thick with foliage that steeply slopes down to the shore of the lake. The lake is located at the foot of Mount Malepunyo, and nearby is Mount Banahaw, in Brgy. Ayusan, in the town of Tiaong. Access to the lake is through Brgy. San Pedro.
Laguna del Maule is a volcanic field in the Andes mountain range of Chile, close to, and partly overlapping, the Argentina–Chile border. The bulk of the volcanic field is in the Talca Province of Chile's Maule Region. It is a segment of the Southern Volcanic Zone, part of the Andean Volcanic Belt. The volcanic field covers an area of 500 km2 (190 sq mi) and features at least 130 volcanic vents. Volcanic activity has generated cones, lava domes, lava coulees and lava flows, which surround the Laguna del Maule lake. The field gets its name from the lake, which is also the source of the Maule River.
Cerro Overo is a volcanic crater in Chile. It lies at the foot of Chiliques volcano and close to Laguna Lejía, over ignimbrites of Pliocene age erupted by the La Pacana volcano. It is 480 by 580 metres wide and 72 metres (236 ft) deep and formed through combined explosive-effusive eruptions. The lavas are of lower crustal provenience and are among the least silicic in the region.
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