Lava delta
Encyclopedia
Lava deltas form wherever sub-aerial flows of lava
enter standing bodies of water. The lava cools and breaks up as it encounters the water, with the resulting fragments filling in the seabed topography such that the sub-aerial flow can move further offshore. Lava deltas are generally associated with large-scale, effusive type basaltic
volcanism
.
as they produce the necessary effusive basaltic flows.
The largest lava delta systems known are associated with formation of volcanic type passive margin
s. Just prior to break-up along the northern Atlantic in the late Paleocene
, massive eruptions occurred along the eventual line of break-up. This volcanism, part of the North Atlantic Igneous Province
, led to the formation of two extensive lava escarpments, interpreted as deltas, extending from the Faeroes onto the Møre Margin (the Faeroe-Shetland escarpment) and the Vøring escarpment on the Vøring margin, a combined distance of approximately 1000 km. As these deltas were prograding into water of relatively constant depth, they were able to extend as much as 25 km from their original vents.
s, fall down to the seabed forming foresets. As the seabed topography becomes infilled, the subaerial flow is able to build out. The process continues as long as the lava supply is maintained. Most lava deltas are formed by relatively low viscosity
Pahoehoe type flows and the lava reaches the sea via a system of small lava tube
s, their entry into the water being marked by a series of steam plumes.
On steep-sided volcanic islands, lava deltas make attractive sites for building and many villages and towns are located on old lava deltas, such as Garachico
on Tenerife
.
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
enter standing bodies of water. The lava cools and breaks up as it encounters the water, with the resulting fragments filling in the seabed topography such that the sub-aerial flow can move further offshore. Lava deltas are generally associated with large-scale, effusive type basaltic
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
.
Occurrence
Lava deltas are found mainly associated with volcanic islands, particularly those formed at hotspotsHotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
as they produce the necessary effusive basaltic flows.
The largest lava delta systems known are associated with formation of volcanic type passive margin
Passive margin
A passive margin is the transition between oceanic and continental crust which is not an active plate margin. It is constructed by sedimentation above an ancient rift, now marked by transitional crust. Continental rifting creates new ocean basins. Eventually the continental rift forms a mid-oceanic...
s. Just prior to break-up along the northern Atlantic in the late Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
, massive eruptions occurred along the eventual line of break-up. This volcanism, part of the North Atlantic Igneous Province
North Atlantic Igneous Province
The North Atlantic Igneous Province is a large igneous province estimated to be at least 1.3 km2 in area and 6.6 km3 in volume. Geographically, the NAIP makes up all of the North Atlantic Ocean as well as the Paleocene and Eocene basalts of Greenland, Iceland, the United Kingdom, Denmark, Norway...
, led to the formation of two extensive lava escarpments, interpreted as deltas, extending from the Faeroes onto the Møre Margin (the Faeroe-Shetland escarpment) and the Vøring escarpment on the Vøring margin, a combined distance of approximately 1000 km. As these deltas were prograding into water of relatively constant depth, they were able to extend as much as 25 km from their original vents.
Formation
When a sub-aerial lava flow reaches the ocean (or other large body of water), contact with the water causes both rapid cooling of the lava and steam explosions that fragment it. The glassy fragments that are formed, known as hyaloclastiteHyaloclastite
Hyaloclastite is a hydrated tuff-like breccia rich in black volcanic glass, formed during volcanic eruptions under water, under ice or where subaerial flows reach the sea or other bodies of water. It has the appearance of angular flat fragments sized between a millimeter to few centimeters...
s, fall down to the seabed forming foresets. As the seabed topography becomes infilled, the subaerial flow is able to build out. The process continues as long as the lava supply is maintained. Most lava deltas are formed by relatively low viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
Pahoehoe type flows and the lava reaches the sea via a system of small lava tube
Lava tube
Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like...
s, their entry into the water being marked by a series of steam plumes.
Hazards
Newly-formed lava deltas can be unstable, especially when they are building out over a steeply sloping seabed. Collapse of the frontal part of lava deltas is common during their formation, representing a hazard for any people that are watching from a solidified part of the delta and such areas are normally marked as dangerous. People standing too close to the edge of an active delta are not only at risk from being thrown in the water but from the steam explosions that accompany the collapse as seawater comes into contact with the active lava tube system.Uses
Garachico
Garachico is a municipality and town on the northern coast of Tenerife, It is located on the TF42 Road about 60km West of the capital Santa Cruz de Tenerife , 50km from Tenerife North Airport and 67 km from Tenerife South Airport. The town itself nestles below a 500m+ cliff...
on Tenerife
Tenerife
Tenerife is the largest and most populous island of the seven Canary Islands, it is also the most populated island of Spain, with a land area of 2,034.38 km² and 906,854 inhabitants, 43% of the total population of the Canary Islands. About five million tourists visit Tenerife each year, the...
.