Rain dust or snow dust, traditionally known as muddy rain, red rain, or coloured rain, is a variety of
rain
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...
(or any other form of
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
) which contains enough
desert dust for the dust to be visible without using a microscope.
History
The rain dust phenomenon was studied by Italian scientist
Giuseppe Maria Giovene
Giuseppe Maria Giovene (23 January 1753 – 2 January 1837) was an Italian archpriest, naturalist, agronomist, geologist, meteorologist, entomologist and ichthyologist. elogio-storico, pag. 9, note 8 He is best known for his studies on the "nit ...
(1753–1837), who managed to correctly explain the phenomenon as early as 1803. On 7 March 1803, rain dust fell over
Southern Italy's region
Apulia. At that time, people believed that the rain was caused by the explosions of Italy's volcanoes
Mount Vesuvius
Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma-stratovolcano located on the Gulf of Naples in Campania, Italy, about east of Naples and a short distance from the shore. It is one of ...
or
Etna, or that it was due to the transport of matter coming from the sea floor and raised by vapor. Giuseppe Maria Giovene related the phenomenon to the wind which occurred prior to the rain event, and he came to the conclusion that the sand had come from Africa and that it had been pushed by the wind coming from south-east.
Geography
Rain dust is common in the Western and Southern Mediterranean, where the dust supply comes from the atmospheric depressions going through the northern part of North Africa. The main sources of desert dust reach the
Iberian Peninsula
The Iberian Peninsula (),
**
* Aragonese and Occitan: ''Peninsula Iberica''
**
**
* french: Péninsule Ibérique
* mwl, Península Eibérica
* eu, Iberiar penintsula also known as Iberia, is a peninsula in southwestern Europe, def ...
and the
Balearic Islands in the form of dust transported by wind or rain from the
Sahara,
Atlas Mountains in
Morocco
Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria t ...
and Central
Algeria
)
, image_map = Algeria (centered orthographic projection).svg
, map_caption =
, image_map2 =
, capital = Algiers
, coordinates =
, largest_city = capital
, relig ...
.
Mud rains are relatively frequent and had been increasing in early 1990s in the
Mediterranean Basin.
It also occurs in arid
desert regions of
North America such as west
Texas
Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
or
Arizona
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
. It occasionally happens in the grasslands as it did in
Bexar County, Texas on March 18, 2008.
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: ]illite
Illite is a group of closely related non-expanding clay minerals. Illite is a secondary mineral precipitate, and an example of a phyllosilicate, or layered alumino-silicate. Its structure is a 2:1 sandwich of silica tetrahedron (T) – alumina ...
, quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
, smectite
A smectite (from ancient Greek ''σμηκτός'' smektos 'lubricated'; ''σμηκτρίς'' smektris 'walker's earth', 'fuller's earth'; rubbing earth; earth that has the property of cleaning) is a mineral mixtures of various swelling sheet sil ...
, palygorskite
Palygorskite or attapulgite is a magnesium aluminium phyllosilicate with the chemical formula ) that occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller's earth. Some smaller deposits of thi ...
, kaolinite, calcite, dolomite and feldspar
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...
s.[ In Majorca a study finds that the size, by volume, 89% of the particles from rain dust fraction corresponded to ]silt
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...
(between 0.002 mm and 0.063 mm) and that there was virtually no clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
sized particles (less than 0.29%).
Importance
* The particulates that rain dust carries are important for the formation of long-term soil
Soil, also commonly referred to as earth or dirt
Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty.
Common types of dirt include:
* Debri ...
counteracting, in large part, the effects of soil erosion. The amount of solids in rain dust have been estimated at 5.3 grams per m2 (in a study made in Montseny
Montseny is a municipality and village in the Vallès Oriental comarca in Catalonia. As of 2014, the population was 332.
The village is located at the feet of the Montseny Massif
Montseny () is a mountain range west of the coastal hills n ...
, Catalonia
Catalonia (; ca, Catalunya ; Aranese Occitan: ''Catalonha'' ; es, Cataluña ) is an autonomous community of Spain, designated as a '' nationality'' by its Statute of Autonomy.
Most of the territory (except the Val d'Aran) lies on the nort ...
) 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 pH of rain water. This may counteract the effects of acid rain.
* Radioactivity from the Chernobyl disaster was carried by rain dust to Greece in 2000.
Blood/red rain
Rain dust is the most common cause of blood rain Blood rain is a phenomenon where blood is perceived to fall from the sky in the form of rain.
Blood Rain may also refer to:
* ''Blood Rain'' (film), a 2005 thriller film
* ''Blood Rain'' (novel), a 1999 crime novel
See also
*''BloodRayne'', a ...
.
Red rain is however not always rain dust, see for example the Red rain in Kerala.
See also
* July 1968 England and Wales dust fall storms
* Alkaline precipitation
References
Bibliography
*
* {{cite book , title=Lettera su di una pioggia rossa , author=Giuseppe Maria Giovene , year=1803, ref=pioggia-rossa
Precipitation
Particulates