bs_bs_banner Jens Esmark’s mountain glacier traverse 1823 À the key to his discovery of Ice Ages GEIR HESTMARK Hestmark, G. 2018 (January): Jens Esmark’s mountain glacier traverse 1823 À the key to his discovery of Ice Ages. Boreas, Vol. 47, pp. 1–10. https://doi.org/10.1111/bor.12260. ISSN 0300-9483. The discovery of Ice Ages is one of the most revolutionary advances made in the Earth sciences. In 1824 Danish- Norwegian geoscientist Jens Esmark published a paper stating that there was indisputable evidence that Norway and other parts of Europe had previously been covered by enormous glaciers carving out valleys and fjords, in a cold climate caused by changes in the eccentricity of Earth’s orbit. Esmark and his travel companion Otto Tank arrived at this insight byanalogous reasoning: enigmatic landscape features theyobserved close to sea level alongtheNorwegian coast strongly resembled features they observed in the front of a retreating glacier during a mountain traverse in the summer of 1823. Which glacier they observed up close has however remained a mystery, and thus an essential piece of information in the story of this discovery has been missing. Based on previously unknown archive sources, supplemented by field study, I here identify the key locality as the glacier Rauddalsbreen. This is the northernmost outlet glacier from Jostedalsbreen, the largest glacier in mainland Europe. Here the foreland exposed byglacier retreat since the Little Ice Age maximum around AD 1750 contains a rich collection of glacial deposits and erosional forms. The point of enlightenment is more precisely identified to be a specific moraine and its distal sandur at 61°53026″N, 7°26043″E. In memoryof Esmark’s travelcompanion who possibly was the first to realise the analogy, it is proposed to name this moraine Otto Tank’s Moraine, a pendant to the already famous Esmark Moraine at Forsand by the sea. Geir Hestmark ([email protected]), Centre for Ecological and Evolutionary Synthesis, CEES, Department of Biosciences, University of Oslo, PO Box 1066 Blindern, Oslo 0316, Norway; received 18th January 2017, accepted 30th March 2017. The discovery of Ice Ages counts amongst the greatest • That along the coast Esmark and his companions discoveries ever made in the Earth sciences (Imbrie & observed several traces and deposits close to sea level Imbrie 1986; Rudwick 2008; Kruger€ 2013). In Norway and far from glaciers, and that at some point they this discovery was due to Jens Esmark (1762–1839), realised that these indicated the former presence of professor of mining sciences at the University of Chris- large glaciers down to sea level: (i) at Forsand, close to tiania (now Oslo), who in late April 1824 published a Stavanger and the entrance of spectacular Lysefjord, paper stating that there was indisputable evidence that they observed a long rampart across a valley, consist- Norway and other parts of Europe had previously been ing of an unsorted mixture of sand, gravel and big covered by enormous glaciers carving out valleys and boulders. This ridge is locally known as Vassrygg and fjords, in a cold climate caused by changes in the was later named the Esmark Moraine (Andersen eccentricityof Earth’s orbit (Esmark1824, 1826). Recent 1954; Worsley 2006; Briner et al. 2014); and (ii) at evaluations hail Esmark as ‘the best candidate as the the Sula archipelago at the entrance of the Sognefjord father of current ice age-theory’ (Kruger€ 2013: p. 450), a presumably glacier-polished conglomerate cliff and his ideas as ‘the first distinctly modern formulation (Hestmark 2009a). of the astronomical theory of long-term climate change’ • That during the subsequent mountain traverse (Berger 2012: p. 109). Esmark’s paper preceded by several Esmark and his companions had occasion to study years the later contributions by Swiss savants Ignaz glaciers up close and what glaciers can do to the Venetz in 1829, Jean de Charpentier in 1834, Karl landscape. Schimper and Louis Agassiz in 1837 (Rudwick 2008; Kruger€ 2013). Yet the genesis of Esmark’sIceAgepaper It has often been assumed that Esmark, faced with the has remained much of a mystery. At crucial points his curious Vassryggen at Forsand, there and then realised narrative is frustratingly parsimonious, and leaves the that it was an ancient moraine, and on the spot developed readercravingformoreinformation.Fromthepaperitself his vision of former large scale glaciations down to sea it is evident: level (e.g. Engen 1985). However, his own text suggests rather that a comparison with extant glaciers during the • That the discovery occurred on a long journey along subsequent mountain traverseprovedcrucial in releasing the south and west coast of Norway in the summer of his train of thought, because, after in detail describing 1823, followed by a traverse over the central Norwe- the Vassryggen and the sandur plain in front of it, he gian mountain chain from the west coast to the proceeds: eastern valleyof Gudbrandsdalen, and a return to the ‘Not only the rampart itself, but the whole horizontal plain too capital Christiania. delivers proofs that there has been [a] glacier, because this plain DOI 10.1111/bor.12260 © 2017 The Authors. Boreas published by John Wiley & Sons Ltd on behalf of The Boreas Collegium This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. 2 Geir Hestmark BOREAS exactly resembles those plains which I found bordering the still extant glaciers between Søndfiord and Lomb in Gudbrandsdalen, Discovery comes to those prepared which I likewise travelled last summer. The resemblance is so ’ striking, that anyone who has an opportunity of making this Esmark s 1824 paper appeared to come out of the blue. comparison, must form the same ideas. I must put forward as Never beforehad he published anything about glaciers or proof of this, that Mr. O. Tank, a skilful young mineralogist, who climate change, and the available sources leave no doubt with me observed the here described rampart and afterwards travelled [with me] to the glaciers mentioned, immediately that he crafted his theory of large scale glaciations from exclaimed to me, without me giving him any pretext, that that observations and deductions made on a field trip lasting rampart by Stavanger had to be a glacier rampart’ (Esmark 1824: 3 months in the summer of 1823. However, I have p. 45; Appendix S1). discovered that by 1823 he had a long history of work This passage – the key passage of discovery À strongly related to climate and glaciers. In a hitherto unknown suggests that the moment of enlightenment occurred not handwritten vitae from 1825, submitted on the occasion down at the coast but rather in front of extant glaciers of his election to the Royal Swedish Academy of Science, during their subsequent mountain traverse. Which Esmark points to a decisive episode from his youth: a brings us to the greatest uncertainty that has up to now land surveyor challenged him from the ground to esti- surrounded Esmark’s discovery: which extant glacier(s) mate the height of the bell tower of Houlbjerg church, didhe andhis companionsvisit,and whatdidtheyobserve Denmark, where Esmark’s father was rector (Esmark atthoseglaciers?IfitistruethattheideaofanIceAgewas 1825). Frustratingly he was not told the trick but only conceived in front of a Norwegian glacier, that certainly referred to a book on geometry. Entering Copenhagen places it amongst the most significant locations in the University in 1784 Esmark soon dropped out of theology history of the Earth sciences. But alas, here the published and into medicine, then studied mineralogy and physics record is scant, because Esmark never published more and learned to measure altitudes by barometers; in 1794 than the cited passage. This dearth of information has led he became a certified land surveyor himself. By then he to much speculation over the years, for instance that the had alsograduated from the mining academy at the silver crucial sites must be in the Jotunheimen mountain range town Kongsberg in Norway, a country in political union (e.g. Andersen 1992). The present paper for the first time with Denmark up to 1814. After further studies at the identifies and documents Esmark’s crucial locality, and mining academies of Freiberg (Saxony) and Schemnitz shows how a number of features of this locality proved (Slovakia) he from 1798 to 1814 served as Assessor in the particularly favourable for his serendipitous discovery. central mining administration at Kongsberg, and a lec- turerin mineralogy,geologyand physics in theassociated Material and methods mining seminar (Bergseminaret). In these years he accumulated a lot of field observations he would only This paper is based on written documents and field later re-interpret and mobilize as Ice Age evidence (see observations. Unpublished documents are available and below). The Rev. Thomas Malthus, famous for his essay can be consulted in public archives, notably the National on population and its significance for Darwin’s theoryof Archive of Norway (Riksarkivet) in Oslo, the archives of natural selection, visited Kongsberg and Esmarkin 1799, the Centre for the History of Science at the Swedish noting: ‘he means to measure all the mountains by Academyof Science, Stockholm, and the County archive the barometer’(Malthus 1966: p. 113). Indeed, in 1800 (Landarkivet) of Fyn, Denmark. To avoid footnotes, the Esmarkascended and measuredTronfjell(1666 m)anda unpublished archive sources are cited in the text similarly peakintheRondanemassif(>2000 m)(Esmark1800).In to published sources, e.g. (Esmark 1832), and listed with 1801 he summited and measured Snøhetta (‘The Snow- author, date and archival location in the References. The cap’, 2286 m a.s.l.), then believed to be the highest discovery of these unpublished sources required exhaus- mountain in Scandinavia (Esmark 1803; Hestmark tive sifting of archive material over several years, a 2009b).