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Mt. Erebus
by Kimberly Stineburg
Physical Geology
Spring 2008         
                                   Mount Erebus and Her Crystals
 

            Mt. Erebus crystals are also known as anorthoclase feldspar, a type of feldspar that consists of aluminum silicate. These are spewed from the only active volcano in Antarctica, Mt. Erebus, a polygenetic stratovolcano. Rich in sodium, potassium and silicate, there is only one other place on the planet where these crystals can be found, Mt. Kenya, Africa. Crystals grow in the magma beneath Erebus and get spit out of the mountain inside glassy volcanic bombs. The glass quickly weathers away leaving the mountainside covered in crystals. These crystals are coveted by almost everyone at McMurdo Station. 

 Below you see a piece of an old bomb with the crystals sticking out the sides, my brother spent many years at McMurdo station and gave me these wonderful samples.

                                                                                                Top View

Bottom View

Close Up

While not an extraordinary mineral, these are extraordinarily large. They form over a long period in the molten lava and then are tossed out of the crater when the lava lake erupts. These crystals are embedded in these bombs and vary in size and shape, but all are of astonishing size for feldspar.

            As recorded in the book “The Heart of the Antarctic”  by Ernest Shackleton (1909) the party also observed around the summit area "lumps of lava, large feldspar crystals, from one to three inches in length, and fragments of pumice; both feldspar' and pumice were in many cases coated with sulfur."         

Mt Erebus is the most active volcano in Antarctica and is a significant source of aerosols and gases to the Antarctic atmosphere. It is a unique volcano to study gas and aerosol emissions because, relative to other volcanoes, Mt Erebus is isolated from man-made contaminants in the atmosphere and because it has a very unusual alkali composition. Mt Erebus is currently the only known active volcano with lava of anorthoclase phonolite, which itself is rather rare. Most volcanoes contain basalt lava; interesting because phonolite is more explosive than basalt.
 

            Erebus is also one of the few volcanoes known to have a convecting lava lake. Because of the alkali nature of the magma, experimental studies would predict that the gases should be CO₂-rich. In addition, studies of dissolved CO₂ in melt inclusions found in olivine crystals have shown that the parental basanite, which evolves by fractional crystallization from the phonolite, have some of the highest CO₂ concentrations to date.

Mt. Erebus is famous for its persistent but low-level activity as the world’s southernmost active volcano. But in 2006, it threw one of its biggest recorded tantrums during its last 165 years. Erebus erupted as much as six times a day, throwing what volcanologists call “bombs,” hot rocks, out of the crater and onto the sides of the 3,794-meter-high volcano.                 

                Unpolished Crystal Pendant

The Other Side~Polished

http://images.travelpod.com/users/i-wander/antarctica_2007.1191822840.cimg7332.jpg
http://www.antarcticconnection.com/antarctic/science/mterebus.shtml
http://www.ees.nmt.edu/Geop/mevo/geochem/co2.html
http://www.antarcticconnection.com/antarctic/news/2007/11507edgedisc.shtml
http://erebus.nmt.edu/geology/evolution.html
http://www.coolantarctica.com/Antarctica%20fact%20file/History/Ernest%20Shackleton_Nimrod_expedition.htm