Ankarana Reserve is a small, partially vegetated plateau in northern Madagascar

Madagascar

The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

 composed of 150-million-year-old middle Jurassic limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

. With an average annual rainfall of about 2000 millimetres (78.7 in), the underlying rocks are susceptible to erosion, thereby producing caves and underground rivers—a karst topography

Karst topography

Karst topography is a geologic formation shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite, but has also been documented for weathering resistant rocks like quartzite given the right conditions.Due to subterranean drainage, there...

. The rugged relief and the dense vegetation have helped protect the region from human intrusion.

The plateau slopes gently to the east, but on the west it ends abrubtly in the "Wall of Ankarana", a sheer cliff that extends 25 kilometres (15.5 mi) north to south, and rises as high as 280 metres (918.6 ft). To the south, the limestone mass breaks up into separate spires known as tower karst. In the center of the plateau, seismic activity and eons of rainfall have dissolved the limestone away in deep gorges, and sometimes redeposited it in ribbons of flowstone

Flowstone

Flowstones are composed of sheetlike deposits of calcite formed where water flows down the walls or along the floors of a cave. They are typically found in "solution", or limestone caves, where they are the most common speleothem. However, they may form in any type of cave where water enters that...

. In places where the calcific upper layers have been completely eroded, the harder base rock has been etched into channels and ridges known as tsingy.

Exploration

Beginning in the 1960s, expatriate Frenchman Jean Duflos (who married locally changed his name to Jean Radofilao) did a huge amount of exploration of the cave systems and subterranean rivers of the Massif, much of it on his own or with visiting speleologists. A total of about 100 kilometres (62.1 mi) of cave passages within the massif have been mapped.
One of the most accessible caves, La Grotte d'Andrafiabe, alone comprises at least 8.035 kilometres (5 mi) of horizonatal passages.

Unique Wildlife

Expeditions that first began cataloguing the animals of Ankarana in the 1980s are described in Dr Jane Wilson-Howarth

Jane Wilson-Howarth

Jane Wilson-Howarth is a British physician, lecturer and author. She has written three travel health guides, two travel narratives and innumerable articles and scientific papers.-Early life:...

's travel narrative Lemurs of the Lost World and in the scientific press. Discoveries included unexpected sub-fossil remains of large extinct lemurs and surviving but previously undescribed species of blind fish, shrimps and other invertebrates. Several expedition members contributed photos to an introductory guide to Madagascar which features the Crocodile Caves. The Ankarana Reserve is an important refuge for significant populations of the crowned lemur

Crowned Lemur

The crowned lemur is a lemur that is 31–36 cm long and weighs 2 kg. Its tail is about 42–51 cm long). The crowned lemur is endemic to the dry deciduous forests of the northern tip of Madagascar. It eats a diet of mostly flowers, fruits, and leaves...

, Sanford's brown lemur

Sanford's Brown Lemur

Sanford's brown lemur , or Sanford's lemur, is a species of prosimian primate in the Lemuridae family. The Sanford's brown lemur was previously considered a subspecies of the common brown lemur but as of 2005 many of the brown lemurs have been elevated to a full species status...

and other mammal species.