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Roger Weller, geology instructor

wellerr@cochise.edu
                                 

Pillow Lavas
Crystal Crow
Historical Geology
Spring 2006
 

PILLOW LAVAS

What are Pillow Lavas?:

Pillow lavas are “elongated lava “pillows” that are formed by repeated oozing and quenching of the hot basalt” (USGS). This procedure is in a 2 step sequence:

  1) A stretchy glassy crust forms on the recent extruded lava, forming an extended pillow,

  2) Pressure builds until the crust breaks and new basalt extrudes like toothpaste, forming another pillow.

      This goes on until the lava is thick and ready to be deposited.  The pillows are described as “bulbous, spherical, or tubular lobes of lava” (Nemo). During the formation, the recent pillows erupt from the and flow outward until they freeze. This process produces  steep-sided mounds or ridges that can grow very thick.

www.earth.northwestern.edu

 

What are the characteristics of a Pillow Lava?:

1) There are chilled glass selvedges around the pillows. This is formed by the rapid cooling of the lava by the water. 

2) They can be the less than 1 meter in diameter or can grow as long as 7 meters.

3) Their shapes can either be sphere- shaped, circular, or compressed in a cross-section.

4) Pillow tops are typically rounded upward, while their undersurfaces may be smooth, curved up or propelled down between underlying pillows.

5) Gas cavities are usually located on the upper part of the pillow lavas.

6) In some instances, clay and sand may be evident between the spaces of the pillows.

7) Pillows are solid and not typically hollow. They frequently have scuff marks on their sides that appear during the extrusion.

              www.env.duke                                              ocean explorer.noaa.gov

 

Where can pillow lavas be found?:

They can be found in oceans, lakes, rivers and glaciers. They have been found in Scotland, United States( Hawaii, Washington State, Oregon), Iceland, Canada,  the island of Crete, and possibly many more.

www.uwsp.edu  picture of a pillow lava in Scotland.     www.divediscover.whoi.edu
                                                                                        pillow lavas in Hawaii.

 

Early Life Found in Pillow Lavas:

Mineralized tubes the size of micrometers were found in pillow lava rims that were in the Mesoarchean Barberton Greenstone Belt that is located in South Africa. These tubes prove that there was submarine microbial action during Earth’s early history. The borders of the tubes hold organic carbon. The overlying of metamorphic and magmatic dating of the pillow lavas imply that microbial life populated these subdivisions of volcanic rocks right after their explosion approximately 3.5 billion years ago.

 

Works Citied

Furnes, Harald, Banerjee R. Neil, Muehlenbachs, Karlis, Staudigel Hubert, de Witt, Maarten.

Early life Recorded in Archean Pillow Lavas.  23 April 2004.

http://www.sciencemag.org/cgi/content/abstract/304/5670/578

Photo glossary of Volcano terms.  2001. http://volcanoes.usgs.gov/Products/Pglossary/PillowLava.html

Pillow Lava.  11 April 2006.

http://www.geo.ua.edu/volcanology/lecture_lecture_notes_files/pillow_lava.html

Pillow Lava. 11 April 2006.

http://volcano.und.nodak.edu/vwdocs/vwlessons/lava/part1.html

Pillow Lava. 11 April 2006.

http://www.pmel.noaa.gov/vents/nemo/explorer/concepts/pillows.html

Pillow Lava. 11 April 2006.

http://www.volcanolive.com/pillow.html