A ponor is a natural opening where surface water enters into underground passages; they may be found in karst landscapes where the geology and the geomorphology is typically dominated by porous limestone rock. Ponors can drain stream or lake water continuously or can at times work as springs, similar to estavelles. Morphologically, ponors come in forms of large pits and caves, large fissures and caverns, networks of smaller cracks, and sedimentary, alluvial drains.
Alea (Greek: Αλέα, before 1928: Μπουγιάτι – Bougiati) is a village and a former community in Argolis, Peloponnese, Greece. Since the 2011 local government reform it is part of the municipality Argos-Mykines, of which it is a municipal unit. The municipal unit has an area of 143.206 km. The seat of the community was Skoteini. Alea is situated in the mountainous northwestern part of Argolis, 5 km southeast of Kandila, 12 km northwest of Lyrkeia, 14 km northeast of Levidi and 27 km north of Tripoli. The Greek National Road 66 (Levidi – Nemea) passes near Skoteini.
In geology, a depression is a landform sunken or depressed below the surrounding area. Depressions form by various mechanisms.
A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water enters into underground passages known as ponor, swallow hole or swallet. A cenote is a type of sinkhole that exposes groundwater underneath. Sink and stream sink are more general terms for sites which drain surface water, possibly by infiltration into sediment or crumbled rock.
Most sinkholes are caused by karst processes – the chemical dissolution of carbonate rocks, collapse or suffosion processes. Sinkholes are usually circular and vary in size from tens to hundreds of meters both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may form gradually or suddenly, and are found worldwide.
Argon Pedion (Greek: Ἀργὸν Πεδίον, lit. 'untilled plain') is the geological name of a "closed karst basin" in the Arcadian highlands in the Peloponnese peninsula of southern Greece. The first known appearance of this name was in a publication by the ancient geographer Pausanias (110–180 AD). He called it untilled plain, because the grassland and acres may be flooded beyond the time when annual vegetation starts. When the winter rains were very heavy, floods can even turn the plain into a temporary lake. Intensive karst formation (drainage in underground waterways of limestone layers) prevents the formation of a permanent lake. In rare cases, even today, modern technologies can not prevent flooding.
A steephead valley, steephead or blind valley is a deep, narrow, flat bottomed valley with an abrupt ending. Such closed valleys may arise in limestone or karst landscapes, where a layer of permeable rock lies above an impermeable substrate such as marl. Water flowing through a steephead valley leaves via one or more ponors or sinkholes.
Blind valleys are typically dry at their lower ends. If the ponor cannot contain the high runoff during a flood event an intermittent flow may continue through the valley beyond the sink. Such a landform is called a semi-blind or half-blind valley.
In karst geology, estavelle or inversac is a ground orifice which, depending on weather conditions and season, can serve either as a sink or as a source of fresh water. It is a type of ponor or sinkhole.