View source for Earth:Kola Superdeep Borehole

{{Short description|Soviet scientific deep drilling project}}
{{Infobox mine
| name                   = Kola Superdeep Borehole
| image                  = File:Кольская сверхглубокая скважина crop.jpg
| width                  = 
| caption                = Superstructure of the Kola Superdeep Borehole, 2007
| pushpin_map            = Russia#Russia Murmansk Oblast
| pushpin_mapsize        = 
| pushpin_map_alt        = 
| pushpin_map_caption    = Location of the borehole in Murmansk Oblast, Russia
| pushpin_image          = 
| pushpin_label          = 
| pushpin_label_position = 
| coordinates            = {{Coord|69.3965|N|30.6100|E|type:landmark_region:RU|display=inline,title}}
| place                  = Pechengsky District
| subdivision_type       = Province
| state/province         = Murmansk Oblast
| country                = {{wipe|Russia}}
| products               = 
| amount                 = 
| financial year         = 
| type                   = Scientific [[Engineering:Borehole|borehole]]
| greatest depth         = {{convert|12262|m|ft}}
| opening year           = 1965
| active years           = {{hlist|1970–1983|1984|1985–1992}}
| closing year           = 1995
| owner                  = 
| official website       = 
| acquisition year       = 
| module                 = 
}}

The '''Kola Superdeep Borehole''' ({{lang-ru|Кольская сверхглубокая скважина|translit=Kol'skaya sverkhglubokaya skvazhina}}) '''SG-3'''{{efn|
SG (СГ) is a Russian designation for superdeep (сверхглубокая) borehole intended to be {{convert|7000|m|ft}} deep. Aralsor SG-1 and Biyikzhal SG-2 preceded the SG-3.
}}
is the result of a [[Earth:Scientific drilling|scientific drilling]] project of the [[Place:Soviet Union|Soviet Union]] in the Pechengsky District, near the Russian border with Norway, on the Kola Peninsula. The project attempted to drill as deep as possible into the [[Earth:Earth's crust|Earth's crust]].
 
Drilling began on 24&nbsp;May 1970 using the ''Uralmash-4E'', and later the ''Uralmash-15000'' series drilling rig, and it became the deepest manmade hole in history in 1979. The {{convert|9|in|cm|order=flip|adj=mid|-diameter}} [[Engineering:Borehole|borehole]]s were drilled by branching from a central hole.<ref name=SmithMag-2015-02-19>{{cite magazine |title=What's the deepest hole ever dug? |date=19 February 2015 |department=Ask Smithsonian |magazine=Smithsonian |publisher=Smithsonian Institution |place=Washington, DC |url=http://www.smithsonianmag.com/smithsonian-institution/ask-smithsonian-whats-deepest-hole-ever-dug-180954349 |last=Ault |first=Alicia}}</ref> The deepest reached {{convert|12262|m|ft mi}} in 1989, the [[Earth:Extremes on Earth#Lowest artificial points|deepest human-made hole]] on Earth, and remains so {{As of|2024|lc=y}}.
 
In terms of [[True vertical depth|true vertical depth]], it remains the deepest [[Engineering:Borehole|borehole]] in the world. For two decades, it was also the world's longest borehole in terms of measured depth along the well bore (that is, borehole length) until it was surpassed in 2008 by the {{convert|12289|m|ft mi|adj=mid|-long}} Al Shaheen Oil Well in Qatar.<ref>{{cite news |title=Sakhalin-1 project drills world's longest extended-reach well |date=29 Jan 2011 |agency=BusinessWire |website=Ordons News |url=https://www.ordons.com/asia/far-east/9976-sakhalin-1-project-drills-worlds-longest-extended-reach-well.html |archive-url=https://web.archive.org/web/20110131190440/http://www.ordons.com/asia/far-east/9976-sakhalin-1-project-drills-worlds-longest-extended-reach-well.html |archive-date=31 January 2011}}</ref>

==Drilling==
[[File:1987 CPA 5892.jpg|thumb|upright|Kola Superdeep Borehole, commemorated on a 1987 USSR stamp]]

Drilling began on 24 May 1970 using the Uralmash-4E, a serial drilling rig used for drilling oil wells. The rig was slightly modified to be able to reach a {{convert|7000|m|ft|adj=on}} depth. In 1974, the new purpose-built Uralmash-15000 drilling rig was installed onsite, named after the new target depth, set at {{convert|15000|m|ft}}.<ref name=Королев-2016-08-06>{{cite web |last=Королев |first=Владимир |date=2016-08-06 |title=Подземное неземное |website=nplus1.ru |url=https://nplus1.ru/material/2016/08/06/Kola-Superdeep-Borehole |access-date=2021-08-08}}</ref>

On 6 June 1979, the world depth record held by the [[Earth:Bertha Rogers|Bertha Rogers]] hole in Washita County, Oklahoma, United States, at {{convert|9583|m|ft}},<ref>{{cite news |title=The KTB borehole – Germany's superdeep telescope into the Earth's crust |date=January 1995 |website=Oilfield Review |url=http://www.slb.com/media/services/resources/oilfieldreview/ors95/jan95/01950422.pdf |access-date=8 April 2009 |archive-url=https://web.archive.org/web/20081219150858/http://www.slb.com/media/services/resources/oilfieldreview/ors95/jan95/01950422.pdf |archive-date=19 December 2008}}</ref> was broken. In October&nbsp;1982, the first hole reached {{convert|11662|m|ft}},<ref name=Яковлев-Скуфьин-Чвыков-2014>{{cite periodical |last1=Яковлев |first1=Ю.Н. |last2=Скуфьин |first2=П.К. |last3=Чвыков |first3=О.С.Ч. |year=2014 |title=Влияние Природных Факторов на Траекторию и Форму Стволов Кольской Сверхглубокой Скважины (СГ-3) |periodical=Вестник Кольского научного центра РАН |volume=2014-03 |pages=8–15 |url=https://www.ksc.ru/docs/vestnik/vestnik-3-2014.pdf |lang=ru}}</ref> and the second hole was started in January&nbsp;1983 from a {{convert|9300|m|ft|adj=on}} depth of the first hole.<ref name=Королев-2016-08-06/>

In 1983, the drill passed {{convert|12000|m|ft}} in the second hole, and drilling was stopped for about a year for numerous scientific and celebratory visits to the site.<ref name="NiZ" />

This idle period may have contributed to a breakdown after drilling resumed; on 27&nbsp;September 1984, after drilling to {{convert|12066|m|ft}}, a {{convert|5|m|ft|adj=off}} section of the drill string twisted off and was left in the hole. Drilling was restarted in September 1986, {{convert|7000|m|ft}} from the first hole.<ref name="NiZ">{{cite web |author=Osadchy, A. |date=2002 |title=Legendary Kola Superdeep |website=Наука и жизнь [Journal of Science and Life] |language=ru |volume=5 |url=http://www.nkj.ru/archive/articles/4172/ |access-date=8 May 2009}}</ref><ref name=Яковлев-Скуфьин-Чвыков-2014/>

The third hole reached {{convert|12262|m|ft}} in 1989.<ref>{{Cite web |date=2023-06-01 |title=Why Is China Drilling a 33,000-Feet Hole in Xinjiang? |url=https://time.com/6284032/china-drill-hole-xinjiang/ |access-date=2023-08-16 |website=Time |language=en}}</ref> In that year, the hole depth was expected to reach {{convert|13500|m|ft}} by the end of 1990 and {{convert|15000|m|ft}} by 1993.<ref>{{cite news |title=Kola Superdeep is in the Guinness Book of World Records |periodical=Zemlya I Vselennaya |year=1989 |number=3 |page=9 |language=ru}}</ref><ref>{{cite web |first1=Adam |last1=Cassino |year=2003 |title=Depth of the deepest drilling |website=hypertextbook.com |series=The Physics Factbook |url=http://hypertextbook.com/facts/2003/AdamCassino.shtml}}</ref>{{Failed verification|date=August 2021}}

In June&nbsp;1990, a breakdown occurred in the third hole at {{convert|12262|m|ft}} of depth. The drilling of the fourth hole was started in January&nbsp;1991 from {{convert|9653|m|ft}} of depth of third hole. The drilling of the fourth hole was stopped in April&nbsp;1992 at {{convert|11882|m|ft}} of depth. Drilling of the fifth hole started in April&nbsp;1994 from {{convert|8278|m|ft}} of depth of the third hole. Drilling was stopped in August&nbsp;1994 at {{convert|8578|m|ft}} of depth due to lack of funds and the well itself was mothballed.<ref name=Яковлев-Скуфьин-Чвыков-2014/><ref name=Khokhlova-2008-10-15/>

During the drilling process, unexpectedly no basaltic layers were found at seven kilometers down or at any depth in the borehole.<ref name="Andrei">{{Cite web |last=Andrei |first=Mihai |date=2014-06-03 |title=The World's Deepest Hole Lies Beneath this Rusty Metal Cap - The Kola Superdeep Borehole |url=https://www.zmescience.com/other/feature-post/worlds-deepest-hole-lies-beneath-rusty-metal-cap-kola-superdeep-borehole/ |access-date=2022-12-28 |website=ZME Science |language=en-US}}</ref>  Prior to that, geological information about the Earth's crust was mostly based on analyzing seismic waves that indicated discontinuity.<ref name="Andrei"/>  Scientific models had previously suggested basalt should be seen.  Instead, the actual geological evidence from the borehole revealed there were more granites, and at much greater depths than scientists had considered.<ref name="Andrei"/>  It was then thought by scientists that seismic discontinuity was caused by granite metamorphosis instead of basalts.<ref name="Andrei"/> In addition to this, water was unexpectedly found at three to six kilometers deep.<ref name="Andrei"/>  Water was not naturally vaporizing at any depth in the borehole.<ref>{{Cite journal |date=March 1995 |title=95/01953 Characterization of crystalline rocks in deep boreholes. The Kola, Krivoy Rog and Tyrnauz boreholes |url=http://dx.doi.org/10.1016/0140-6701(95)93618-1 |journal=Fuel and Energy Abstracts |volume=36 |issue=2 |pages=133 |doi=10.1016/0140-6701(95)93618-1 |issn=0140-6701}}</ref> Instead, water was found at these greater depths.<ref>{{Cite journal |date=March 1995 |title=95/01953 Characterization of crystalline rocks in deep boreholes. The Kola, Krivoy Rog and Tyrnauz boreholes |url=http://dx.doi.org/10.1016/0140-6701(95)93618-1 |journal=Fuel and Energy Abstracts |volume=36 |issue=2 |pages=133 |doi=10.1016/0140-6701(95)93618-1 |issn=0140-6701}}</ref> Scientific models previously had not predicted water to be found at such great depths.<ref>{{Cite web |title=Scientists have discovered a sea of fresh water under the ocean |url=https://www.weforum.org/agenda/2019/06/scientists-have-discovered-a-sea-of-fresh-water-under-the-ocean/ |access-date=2022-12-28 |website=World Economic Forum |language=en}}</ref>  It was discovered that deep granites can be fractured and receive water this deep.<ref>{{Cite web |title=Where is Earth's Water? {{!}} U.S. Geological Survey |url=https://www.usgs.gov/special-topics/water-science-school/science/where-earths-water |access-date=2022-12-28 |website=www.usgs.gov}}</ref> As a result of these findings, many scientists now theorize that aquifers of water can be found at much greater depths than older scientific models had previously thought possible.<ref>{{Cite journal |last1=Kozlovskiy |first1=Ye. A. |last2=Clarke |first2=J. W. |last3=McDowell |first3=R.C. |last4=Matzko |first4=J.R. |last5=Hearn |first5=P.P. |last6=Milton |first6=D.J. |last7=Percious |first7=D.J. |last8=Vitaliano |first8=D.B. |last9=Ulmishek |first9=Gregory |date=1986 |title=The Kola, USSR, superdeep drill hole |journal=Open-File Report |doi=10.3133/ofr86517 |issn=2331-1258|doi-access=free }}</ref><ref>{{Cite journal |date=March 1995 |title=95/01953 Characterization of crystalline rocks in deep boreholes. The Kola, Krivoy Rog and Tyrnauz boreholes |url=http://dx.doi.org/10.1016/0140-6701(95)93618-1 |journal=Fuel and Energy Abstracts |volume=36 |issue=2 |pages=133 |doi=10.1016/0140-6701(95)93618-1 |issn=0140-6701}}</ref><ref name="Andrei"/>

==Research==
The Kola Superdeep Borehole penetrated about a third of the way through the [[Place:Baltic Shield|Baltic Shield]] [[Earth:Continental crust|continental crust]], estimated to be around {{convert|35|km|mi}} deep, reaching [[Earth:Archean|Archean]] rocks at the bottom.<ref>{{cite book |author1=Ramberg, I.B. |author2=Bryhni, I. |author3=Nøttvedt, A. |name-list-style=amp |year=2008 |title=The Making of a Land: Geology of Norway |publisher=Geological Society |isbn=978-82-92394-42-7 |page=624 |url=https://books.google.com/books?id=rMVNE0F2SckC&pg=PA76 |access-date=27 January 2010}}</ref> The project has been a site of extensive geophysical examinations. The stated areas of study were the deep structure of the Baltic Shield, seismic discontinuities and the thermal regime in the Earth's crust, the physical and chemical composition of the deep crust and the transition from upper to lower crust, lithospheric geophysics, and to create and develop technologies for deep geophysical study.

To scientists, one of the more fascinating findings to emerge from this well is that no transition from [[Chemistry:Granite|granite]] to [[Earth:Basalt|basalt]] was found at the depth of about {{convert|7|km|mi|spell=in}}, where the velocity of seismic waves has a discontinuity. Instead, the change in the seismic wave velocity is caused by a metamorphic transition in the granite rock. In addition, the rock at that depth had been thoroughly fractured and was saturated with water, which was surprising. This water, unlike surface water, must have come from deep-crust minerals and had been unable to reach the surface because of a layer of impermeable rock.<ref>{{cite web |author=Bellows, Alan |date=5 March 2007 |title=The Deepest Hole |website=Damn Interesting |url=http://www.damninteresting.com/the-deepest-hole/ |access-date=27 December 2014}}</ref>

Microscopic plankton fossils were found {{convert|6|km|mi|spell=in}} below the surface.<ref name=SmithMag-2015-02-19/>

Another unexpected discovery was a large quantity of [[Chemistry:Hydrogen|hydrogen]] gas. The drilling mud that flowed out of the hole was described as "boiling" with hydrogen.<ref>{{cite conference|author=G. J. MacDonald|date=1988|title=Major Questions About Deep Continental Structures|book-title=Deep drilling in crystalline bedrock, v. 1| editor=A. Bodén and K. G. Eriksson|publisher=[[Physics:Springer-Verlag|Springer-Verlag]]|location=Berlin|pages=28–48|isbn=978-3-540-18995-4}}</ref>

In 1992, an international geophysical experiment obtained a reflection seismic crustal cross-section through the well. The Kola-92 working group consisted of researchers from the universities of [[Organization:University of Glasgow|Glasgow]] and [[Organization:University of Edinburgh|Edinburgh]] in the United Kingdom, the [[Organization:University of Wyoming|University of Wyoming]] in the United States, and the University of Bergen in Norway, as well as several Russian earth science research institutions.<ref>
{{cite journal
 |last1=Smythe        |first1=D.K.         |last2=Smithson   |first2=S.B.
 |last3=Humphreys     |first3=C.           |last4=Gillen     |first4=C.
 |last5=Kristoffersen |first5=Y.           |last6=Karaev     |first6=N.A.
 |last7=Garipov       |first7=V.Z.         |last8=Pavlenkova |first8=N.I.
 |date=1994
 |title=Project images crust, collects seismic data in world's largest borehole
 |journal=Eos, Transactions American Geophysical Union
 |volume=75 |issue=41 |pages=473–476
 |doi=10.1029/94EO01089 |issn=2324-9250
 |language=en
 |url=http://www.davidsmythe.org/professional/pdf/1994%20smythe%20etal%20kola92%20project%20eos.pdf
}}
</ref>
The experiment was documented in a video recorded by Professor David Smythe,<ref>
{{cite AV media
 |title=Crustal seismic reflection profiling through the Kola superdeep well, Russia
 |year=1992
 |people=Smythe, D.K. (videographer)
 |url=https://www.youtube.com/watch?v=9Xrr-pVOjLA |via=[[Company:YouTube|YouTube]] |medium=video
}}
</ref>
which shows the drilling deck in action during an attempt to recover a tool dropped down the hole.

==Status==
{{multiple image
 |align=right |direction=vertical |width=
 |image1=Кольская сверхглубокая скважина (2012).jpg |caption1=The borehole site in 2012
 |image2=Сама скважина(заварена), август 2012.JPG |caption2=The borehole (welded shut), August&nbsp;2012
}}
The drilling terminated in 1995 due to a lack of funds.<ref name=Khokhlova-2008-10-15>{{cite web |author=Khokhlova, Galina |date=15 October 2008 |title=Гордость пойдет в утиль: Кольская сверхглубокая скважина будет ликвидирована |language=ru |trans-title=Pride goes to waste: Kola superdeep borehole to be scrapped |website=Российская Газета [Rossiyskaya Gazeta] |url=http://www.rg.ru/2008/10/15/skvazhina.html |access-date=9 July 2010}}</ref> The scientific team was transferred to the federal state unitary subsidiary enterprise "Kola Superdeep", reduced and reoriented to a thorough study of the exposed section.<ref name=Яковлев-Скуфьин-Чвыков-2014/> In 2007, the scientific team was dissolved and the equipment was transferred to a private company and partially liquidated.<ref name=Яковлев-Скуфьин-Чвыков-2014/>

In 2008, the company was liquidated due to unprofitability,<ref>{{cite news |title=Росимущество ликвидирует самую глубокую скважину в мире |date=2008-04-10 |url=https://lenta.ru/news/2008/04/10/skvazh/ |access-date=2021-08-08 |website=lenta.ru |language=ru}}</ref> and the site was abandoned. The site is still visited by curious sightseers, who have reported that the structure over the borehole has been partially destroyed or removed.<ref name="AO">{{cite web |title=Kola superdeep borehole, Murmansk, Russia |url=https://www.atlasobscura.com/places/kola-superdeep-borehole?mc_cid=69025636df&mc_eid=34be11d5e3 |access-date=14 August 2020 |website=Atlas Obscura}}</ref>

==Similar projects==
* The United States had embarked on a similar project in 1957, dubbed [[Earth:Project Mohole|Project Mohole]], which was intended to penetrate the shallow crust under the Pacific Ocean off of Mexico. After initial drilling, the project was abandoned in 1966 when funding was cut off. This program inspired the Ocean Drilling Program, Integrated Ocean Drilling Program, and the present [[Organization:International Ocean Discovery Program|International Ocean Discovery Program]].
* The KTB superdeep borehole ([[Engineering:German Continental Deep Drilling Programme|German Continental Deep Drilling Programme]], 1987–1995) at Windischeschenbach in northern Bavaria was drilled to a depth of {{convert|9101|m|ft}}, reaching temperatures of more than {{convert|260|°C|°F}}. Its ambitious measuring program used high-temperature logging tools that were upgraded specifically for KTB.<ref>
{{cite journal
 |last1=Emmermann  |first1=Rolf
 |last2=Lauterjung |first2=Jörn
 |year=1997
 |title=The German continental deep drilling program KTB: Overview and major results
 |journal=Journal of Geophysical Research: Solid Earth
 |volume=102  |issue=B8  |pages=18179–18201
 |doi=10.1029/96JB03945 |doi-access=free
 |bibcode=1997JGR...10218179E |issn=2156-2202
 |language=en
 |url=http://userpage.fu-berlin.de/geodyn/tutorials/Praktikum/pdf/Emmermann-etal1997_JGR.pdf
 |archive-url=https://web.archive.org/web/20121030115502/http://userpage.fu-berlin.de/geodyn/tutorials/Praktikum/pdf/Emmermann-etal1997_JGR.pdf
 |archive-date=30 October 2012
}}</ref>
* In 2023, China embarked on a 10,000 m super-deep borehole in the Tarim Basin in the [[Place:Xinjiang|Xinjiang]] region for scientific, oil and gas exploration.<ref name="Cheung2023">{{Cite web |title=China begins drilling one of world’s deepest holes in hunt for discoveries deep inside the Earth |first=Rachel |last=Cheung |work=the Guardian |date=6 June 2023 |access-date=10 June 2023 |url= https://www.theguardian.com/world/2023/jun/06/china-begins-drilling-one-of-worlds-deepest-holes-in-hunt-for-discoveries-deep-inside-the-earth |quote=China has begun digging its deepest borehole in an effort to study areas of the planet deep beneath the surface. The drilling of the borehole began on Tuesday in a desert in the Tarim basin in China’s north-western region of [[Place:Xinjiang|Xinjiang]], according to the Chinese state-run Xinhua news agency. With a planned depth of 11,100 metres, the narrow shaft will penetrate more than 10 continental strata and reach the cretaceous system in the Earth’s crust – a series of stratified rocks dating back 145 million years.}}</ref><ref name="Sharma2023">{{Cite web |title=China's 10,000-meter deep dive into scientific exploration |last=Sharma |first=Sejal |work=interestingengineering.com |date=31 May 2023 |access-date=10 June 2023 |url= https://interestingengineering.com/innovation/chinas-10000-meter-deep-dive-into-scientific-exploration}}</ref><ref name="SkyNews2023">{{Cite web |title=China drilling hole over 11,000m deep into the desert |author=Sky News |work=Sky News |date=2 June 2023 |access-date=10 June 2023 |url= https://news.sky.com/story/china-drilling-hole-over-11-000m-deep-into-the-desert-12894901}}</ref>

==Records==
The Kola Superdeep Borehole was both the longest and deepest borehole in the world from 1989 to 2008.<ref name=SmithMag-2015-02-19/> In May&nbsp;2008, the Kola Superdeep Borehole's record length (but not record depth) was surpassed by a curved borehole of the [[Engineering:Extended reach drilling|extended reach drilling]] well BD-04A in the Al Shaheen Oil Field in Qatar, with a total length of {{convert|12289|m|ft}} and a horizontal reach of {{convert|10902|m|ft}}.<ref>
{{cite press release
 |title=Transocean GSF rig&nbsp;127 drills deepest extended-reach well
 |date=21 May 2008
 |publisher=Transocean Ltd.
 |url=http://www.deepwater.com/fw/main/Transocean-GSF-Rig-127-Drills-Deepest-Extended-Reach-Well-283C4.html |access-date=15 November 2010 |url-status=dead
 |archive-url=https://web.archive.org/web/20101112192456/http://www.deepwater.com/fw/main/Transocean-GSF-Rig-127-Drills-Deepest-Extended-Reach-Well-283C4.html
 |archive-date=12 November 2010
}}
</ref><ref>
{{cite news
 |title=Maersk Oil finished Drilling (BD-04A) well at Al-Shaheen field, Qatar
 |date=23 May 2008
 |website=Gulf Oil & Gas Marketplace
 |url=http://www.gulfoilandgas.com/webpro1/main/mainnews.asp?id=6050
 |access-date=15 November 2010
}}
</ref> In terms of depth below the surface, the Kola Superdeep Borehole SG-3 retains the world record at {{convert|12262|m|ft}} reached in 1989 and is still the deepest artificial point on Earth.<ref>
{{cite web
 |title=Kola Superdeep Borehole (KSDB)
 |work=ICDP
 |url=http://www-icdp.icdp-online.org/front_content.php?idcat=695
 |access-date=21 July 2017 |url-status=dead
 |archive-url=https://web.archive.org/web/20140507113717/http://www-icdp.icdp-online.org/front_content.php?idcat=695
 |archive-date=7 May 2014
}}
</ref>

==See also==
* {{annotated link|Earth:Chikyū}}, deep oceanic drilling ship, which achieved a subsea drilling record in 2012
* {{annotated link|Earth:Earthscope}}
* {{annotated link|Earth:Extremes on Earth|Extreme points of Earth}}
* {{annotated link|Earth:Lake Vostok}}
* {{annotated link|Earth:Mohorovičić discontinuity}}
* {{annotated link|Earth:San Andreas Fault Observatory at Depth}}
* [[Vertical seismic profile]] — relevant seismic measurements
* {{annotated link|Unsolved:Well to Hell}} - observed since 1995

== Notes ==
{{notelist}}

==References==
{{reflist|25em}}

==Further reading==
* {{Cite book|last1=Fuchs|first1=K.|author2=Kozlovsky, E.A.|author3=Krivtsov, A.I.|author4=Zoback, M.D.|name-list-style=amp|title=Super-Deep Continental Drilling and Deep Geophysical Sounding|date=1990|publisher=Springer Verlag|location=Berlin|isbn=978-0-387-51609-7|page=436}}
* {{Cite book|last1=Kozlovsky|first1=Ye.A|title=The Superdeep Well of the Kola Peninsula|url=https://archive.org/details/superdeepwellkol00kozl|url-access=limited|date = 1987|publisher=Springer Verlag|location=Berlin|isbn=978-3-540-16416-6|page=[https://archive.org/details/superdeepwellkol00kozl/page/n563 558] }}

==External links==
* [http://superdeep.pechenga.ru/ Official Kola Superdeep Borehole website] {{in lang|ru}}
* [https://www.gi.alaska.edu/alaska-science-forum/worlds-deepest-hole The World's Deepest Hole – Alaska Science Forum – July 1985]
* [http://www.damninteresting.com/?p=567 The Deepest Hole] 20 June 2006
* [http://nauka.relis.ru/06/0205/06205036.htm Kola Superdeep – Scientific research results and experiences by PhD A. Osadchikh] 1984 {{in lang|ru}}
* [http://alexeyzaytsev.ru/2017/10/26/kola-superdeep/ Photo report on a trip to the Kola superdeep well in 2017]. Many photos of the current state. {{in lang|ru}}


[[Category:Structure of the Earth]]

{{Sourceattribution|Kola Superdeep Borehole}}