Rain dust
Encyclopedia
Rain dust or snow dust, traditionally known as muddy, red, coloured or blood rain
, is a rain
or any other form of precipitation
which contains enough desert dust
for the dust to be visible without using a microscope. Rain dust is common in the Western Mediterranean. Dust supply comes from the atmospheric depressions going through the northern part of North Africa.
Rain dust is the most common type of blood rain
. Mud rains are relatively frequent and have been increasing in recent years in the Mediterranean Basin
. Red rain is however not always a rain dust (see the example of Red rain in Kerala
).
and the Balearic Islands
in the form of dust transported by wind or rain from the Western Sahara
, Atlas Mountains
in Morocco
and Central Algeria
.
, quartz
, smectite, palygorskite
, kaolinite
, calcite
, dolomite
and feldspar
s. In Majorca a study finds that the size, by volume, 89% of the particles from rain dust fraction corresponded to silt
(between 0.002 mm and 0.063 mm) and that there was virtually no clay
sized particles (less than 0.29%).
Blood rain
Blood rain or red rain is a phenomenon in which blood is perceived to fall from the sky in the form of rain. Cases have been recorded since Homer's Iliad, composed ca eighth century BC, and are widespread. Before the 17th century it was generally believed that the rain was actually blood...
, is a rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
or any other form of precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
which contains enough desert dust
Mineral dust
Mineral dust is a term used to indicate atmospheric aerosols originated from the suspension of minerals constituting the soil, being composed of various oxides and carbonates. Human activities lead to 30% of the dust load in the atmosphere...
for the dust to be visible without using a microscope. Rain dust is common in the Western Mediterranean. Dust supply comes from the atmospheric depressions going through the northern part of North Africa.
Rain dust is the most common type of blood rain
Blood rain
Blood rain or red rain is a phenomenon in which blood is perceived to fall from the sky in the form of rain. Cases have been recorded since Homer's Iliad, composed ca eighth century BC, and are widespread. Before the 17th century it was generally believed that the rain was actually blood...
. Mud rains are relatively frequent and have been increasing in recent years in the Mediterranean Basin
Mediterranean Basin
In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...
. Red rain is however not always a rain dust (see the example of Red rain in Kerala
Red rain in Kerala
The Kerala red rain phenomenon was a blood rain event that occurred from July 25 to September 23, 2001, when red-coloured rain sporadically fell on the southern Indian state of Kerala. Heavy downpours occurred in which the rain was colored red, staining clothes pink. Yellow, green, and black rain...
).
Source
The main sources of desert dust reach the Iberian PeninsulaIberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...
and the Balearic Islands
Balearic Islands
The Balearic Islands are an archipelago of Spain in the western Mediterranean Sea, near the eastern coast of the Iberian Peninsula.The four largest islands are: Majorca, Minorca, Ibiza and Formentera. The archipelago forms an autonomous community and a province of Spain with Palma as the capital...
in the form of dust transported by wind or rain from the Western Sahara
Western Sahara
Western Sahara is a disputed territory in North Africa, bordered by Morocco to the north, Algeria to the northeast, Mauritania to the east and south, and the Atlantic Ocean to the west. Its surface area amounts to . It is one of the most sparsely populated territories in the world, mainly...
, Atlas Mountains
Atlas Mountains
The Atlas Mountains is a mountain range across a northern stretch of Africa extending about through Morocco, Algeria, and Tunisia. The highest peak is Toubkal, with an elevation of in southwestern Morocco. The Atlas ranges separate the Mediterranean and Atlantic coastlines from the Sahara Desert...
in Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
and Central Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...
.
Dust composition
The rain dust is very alkaline. Some of the large particles contain mixtures of chemicals such as sulfate and sea salt (chiefly with sodium, chlorine and magnesium). Major minerals in order of decreasing abundance are: illiteIllite
Illite is a non-expanding, clay-sized, micaceous mineral. Illite is a phyllosilicate or layered alumino-silicate. Its structure is constituted by the repetition of tetrahedron – octahedron – tetrahedron layers. The interlayer space is mainly occupied by poorly hydrated potassium cations...
, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, smectite, palygorskite
Palygorskite
Palygorskite or attapulgite is a magnesium aluminium phyllosilicate with formula 2Si4O10·4 which occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller's earth.-Name:...
, kaolinite
Kaolinite
Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra...
, calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
, dolomite
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
and feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
s. In Majorca a study finds that the size, by volume, 89% of the particles from rain dust fraction corresponded to silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
(between 0.002 mm and 0.063 mm) and that there was virtually no clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
sized particles (less than 0.29%).
Importance
- The solid matters that rain dust brings are important for the formation of long-term soilSoilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
, counteracting, in large part the effects of soil erosion. The amount of solids provided by the rain dust has been estimated at 5.3 grams per m2 (in a study made in MontsenyMontsenyMontseny is a mountain range west of the coastal hills north of Barcelona. It is part of the Catalan Pre-Coastal Range.-Features:The Montseny massif is located within a triangle formed by the AP-7, C-17 and C-25 roads. It has the highest mountains in the area south of the Pyrenees and dominates...
, CataloniaCataloniaCatalonia is an autonomous community in northeastern Spain, with the official status of a "nationality" of Spain. Catalonia comprises four provinces: Barcelona, Girona, Lleida, and Tarragona. Its capital and largest city is Barcelona. Catalonia covers an area of 32,114 km² and has an...
) in this location the dust provides 34% of the calcium needed by the holm oak. The amount of the deposition of dust particles is highly variable depending on the year. - Saharan dust significantly increases the pHPHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of rain water. This may counteract the effects of acid rainAcid rainAcid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions . It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of carbon dioxide, sulfur dioxide and nitrogen...
. - Some radioactivity in rain dust falls to Greece in 2000 was caused by the Chernobyl disasterChernobyl disasterThe Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...
.