In the previous blog post, we introduced the concept of Deep Time and contrasted it with our human time horizon. We will now examine landscape changes that, while slow from a human perspective, occur rapidly compared to geological changes. To do this, we travel to the Black Forest and the Vosges.
There are 30 glacial cirque lakes – or tarns – in the Black Forest (Germany) and the Vosges (France). (Learn more)
These lakes are relatively small and have an almost circular outline – with a maximum diameter of 200 meters. The Wildsee in the Black Forest National Park is one of them.
Moon rise over the Wildsee.
The formation of the tarns
These lakes are relicts of the last glacial period.
This epoch of Earth history lasted about 100 000 years and ended about 12 000 years ago. Within this period, the temperates changed to a certain extend, but overall a much colder climate dominated.
During the last glacial maximum, about 21 000 years ago, the highest regions of the Black Forest and the Vosges (about 1500 meters altitude) were covered by mighty glaciers.
On the highest mountains – like the Feldberg in the Black Forest – the ice cap was shaped as a relatively thin layer of firn. However, in the valleys that originated from these mountains glaciers several hundred meters thick formed. The map shows the situation as it appeared at that time (by courtesy of Dr. Charlotte Prud'homme, Université de Lorraine).
Central Europe during the last glacial maximum about 21 000 years ago. Yellow patches represented areas of loess and loess derivates. Dry continental shelves are represented by beige-coloured areas. Source: Prud'homme, Charlotte and Fischer, Peter and Jöris, Olaf and Gromov, Sergey and Vinnepand, Mathias and Christine, Hatté and Vonhof, Hubert and Moine, Olivier and Vött, Andreas and Fitzsimmons, Kathryn (2022): Millennial-timescale quantitative estimates of climate dynamics in central Europe from earthworm calcite granules in loess deposits. Communications Earth and Environment, Vol 3, DOI: 10.1038/s43247-022-00595-3.
The map shows the expansion of the continental glaciers during the last glacial maximum about 21 000 years ago. (Learn more)
You can clearly spot the ice caps of the southern Black Forest and the Vosges. As a comparison: The glacier covering the Feldberg region in the southern Black Forest had a dimension comparable to the size of today's Hofsjökull glacier in Iceland.
Because of the map’s large spatial scale, the following details cannot be resolved: In the northern Black Forest, the Hornisgrinde massif (1160 meters above sea level, about 80 km north of the Feldberg) was covered by a small glacier, from which two smaller valley glaciers flowed eastward. (Learn more)
At the other higher summits – in most cases on the northern and eastern slopes – individual firn areas formed. Even during summer, the ice didn’t melt there and, simply speaking, shaped depressions into the rock surface. In these depressions – also referred to as cirques – water accumulated after the glaciers melted down. On the opposite side of the slope, in many cases the ice had banked up a moraine that prevented the water from flowing downward into the valley.
That way, the glacial cirque lakes (tarns) were created. In the warmer phase following the last glaciation – an interglacial we call the Holocene – humans began to evolve as a settled species, learned how to practice agriculture and developed urban civilizations. (Learn more)
The whole part of human history from which we have written tradions at our disposal is located in the Holocene. This interglacial period is still ongoing today.
The following figure shows the Huzenbacher See in the Black Forest.
The Huzenbacher See.
In this picture you can clearly recognize the typical landform of a glacial cirque. In a certain sense, the lake is nestled like on a sofa, whereas the backrest – from the highest point of which the photo was taken – is flanked by two ridges (the armrests) that extend away from the viewer towards the valley, starting at the opposite side of the slope.
It is plausible to assume that at the end of the last glaciation, there existed many more glacial cirque lakes than today. Presumably, in the northern Black Forest existed about 40 such lakes. Most of them disappeared during the Holocene through a process called siltation. During this process, a lake is transformed into a swamp and – finally – dries ou completely.
Siltation is the gradual filling of still waters with organic material. As plants slowly grow, the free water surface diminishes over time, and often floating islands of turf form which, in the course of time, are colonized by bushes and even trees. You can clearly see this in the photograph of the Huzenbacher See.
The depressions that no longer contain a lake still exist as well. These bowl-shaped landforms that are open on one side – glacial cirques – can be clearly identified on topographic maps.
The following map shows the topography of the region containing Huzenbacher See.
Topographic map showing the region containing Huzenbacher Sees, northern Black Forest. Map source: LGL, www.lgl-bw.de.
The form of the cirque can be compared to a crater opened to one side.
South east of Huzenbacher See, you notice two further cirques. According to the geograph Fritz Fezer (Learn more), thousands of years ago these cirques housed lakes. We discuss this in detail in a minute.
An interesting detail: Most cirques in the Black Forest and the Vosges are open to the north or east. This is related to the fact that already during the last glaciation the wind mainly came from the west (Atlantic). As a result, the firn areas formed mainly at the northern or eastern slopes of the mountains – the leeside of the mountain.
The following photograph shows a view to the Kammerloch cirque marked on the previous map. The ground of this cirque is named Schwarzmiss.
View into the Kammerloch cirque.
The Schwarzmiss ground is today dried out and covered with dense forest.
The following photograph shows the Schurmsee in northern Black Forest.
Today, the Schurmsee is surrounded by dense forest. Pollen analysis (as discussed in the next blogpost) shows that this might not always have been the case.
Near Schurmsee lies a cirque named Blindsee (translates to: blind lake; see map below). It likely once held a lake, thousands of years ago.
Topographic map showing the region containing Schurmsees. Map source: LGL, www.lgl-bw.de.
The following photograph shows the cirque ground of the Blindsee.
On the cirque ground of the Blindsee.
Landscape changes during the Holocene
The German geographer Fritz Fezer (1924 – 2018) has studied and documented the cirques and tarns in the northern Black Forest in great detail. Based on countless site inspections, he classified all cirques along geomorphological criteria and documented his findings in an article in 1957. (Learn more)
In doing so, he inferred, for example, from the degree of preservation of the moraine the likelihood that a cirque that has since dried out was filled with water in the past.
The following figure shows the geographical locations of the tarns that still exist today .
Tarns in the Black Forest today. Source for the relief map: LGL, www.lgl-bw.de. Information on cirques and tarns are based on Fezer, Fritz (1957): Eiszeitliche Erscheinungen im nördlichen Schwarzwald. Selbstverlag der Bundesanstalt für Landeskunde und Woldstedt, Paul and Schwarzbach, Martin (Hrsg.) (1967): Eiszeitalter und Gegenwart: Jahrbuch der Deutschen Quartärvereinigung, Volume 18, Hohenlohe'sche Buchhandlung Ferd. Rau, Öhringen, Württemberg. The size of the dots is symbolic and not to scale; it does not indicate the actual extent of the respective lake (essentially comprising cirques of group 10 according to Fezer (1957)).
The following figure represents the situation at the beginning of the Holocene several millennia ago (according to the classification of Fezer).
Tarns in the Black Forest at the beginning of the Holocene (according to Fezer). Source for the relief map: LGL, www.lgl-bw.de. Information on cirques and tarns are based on Fezer, Fritz (1957): Eiszeitliche Erscheinungen im nördlichen Schwarzwald, Selbstverlag der Bundesanstalt für Landeskunde und Woldstedt, Paul and Schwarzbach, Martin (Hrsg.) (1967): Eiszeitalter und Gegenwart: Jahrbuch der Deutschen Quartärvereinigung, Volume 18, Hohenlohe'sche Buchhandlung Ferd. Rau, Öhringen, Württemberg. The size of the dots is symbolic and not to scale; it does not indicate the actual extent of the respective lake (essentially comprising cirques of groups 10, 9 and 8 according to Fezer (1957)).
Even though it is difficult to find historical evidence of lakes that have since disappeared, human memory and the knowledge transferred orally from generation to generation may play a role in reconstructing the history of the tarns.
Therefore, Fritz Fezer did not only consider geomorphological criteria in his work, but also historical and other aspects. To get an idea of which of the lakes that existed at the beginning of the Holocene might still have existed during historical time (and have since disappeared), he also considered toponymy. If a cirque had a name that contained a word suggesting the presence of water – for example, Weiher (pond) or See (lake) – in his view, this indicated that a lake still existed in historical times, but has since disappeared. (Learn more):
Fezer wrote in 1957 (Learn more):
The still dark lakes of the Black Forest form a particular attraction. Deeply embedded in the wooded mountains, remote and far away from streets and villages, they surprise the hiker after he has feasted his eyes on the immense Buntsandstein elevations. In similar depressions, at least in spring, he might find puddles of water. On the map, there are names such as 'Blinder See' or 'Weiher'. They indicate that some few centuries ago a lake once existed here. The names of other basins contain the word 'Misse', which means 'marshy spot'. But the swamps are today drained and planted with spruce.
On topographic maps of the Black Forest, you often find locations with a name containing the word 'misse'. As Fezer writes, this word possibly had the meaning 'marshy spot' or 'moor'. It also can have its origin in the Early New High German '-miss' with the meaning 'bad' or 'lousy'. Cf. Early New High German online dictionary at https://fwb-online.de/.
Furthermore, in his work, the aspect of personal memory is of a certain importance – for example, when Fezer reports about the cirque Alter Weiher near Freudenstadt in the following way (Learn more):
In the description of the Freudenstadt district (Oberamt Freudenstadt) published in 1858, the lake is described as a silted-up, 'amphitheater-shaped basin' and is referred to as 'a peat bog overgrown with moss'. However, an elderly resident of Reinerzau told me that during his youth there was still an open pool with an area of approximately 10 $m^2$. Today, this pool has shrunk to about 1 $m^2$ and is covered by a floating peat mat.
The elderly resident mentioned by Fritz Fezer might have been an adolescent end of the 19th century.
The botanist Gerhard Lang (1924 – 2016) writes about the Alter Weiher cirque (referring to Fritz Fezer): (Learn more)
The remotely located and difficult to access Alte Weiher is, according to Fezer (1957), one of the most beautiful cirques in the northern Black Forest – at least in terms of geomorphology …
Referring to the hydrogeographer Wilhelm Halbfaß (1856 – 1938), Gerhard Lang continues:
The boggy soil is still so spongy today that a seven-meter-long pole can be pushed in effortlessly and a grazing cow is said to have sunk in it just 20 years back.
A modern view on cirque studies
Up to this point, I have referred primarily to the somewhat older work of Fritz Fezer. Without intending in any way to diminish this significant achievement, a note from today's perspective is nevertheless appropriate.
To determine whether a lake had existed in a cirque during historical or prehistoric times, Fezer applied a range of criteria drawn from different disciplines, including geomorphology, toponymy, and oral tradition. I have followed his line of argument and sought to highlight the plausibility of his conclusions.
In the interest of scientific rigor, however, it should be emphasized that these plausible conclusions do not constitute sufficient proof that a particular cirque contained a lake during historical or prehistoric times.
To answer this question reliably for such a location, sediment cores would need to be obtained from the floor of the cirque. The discovery of lacustrine sediments, particularly varved deposits, would provide reliable evidence for the former existence of a lake.
To my knowledge, such investigations have not been carried out for all cirques in the Black Forest and the Vosges. Consequently, the question cannot yet be answered with conclusive evidence, and the map presented above (showing the situation at the beginning of the Holocene) should be regarded as a plausible, but ultimately unproven, hypothesis. They remain valid unless they are falsified by evidence from a specific cirque.
I would like to thank geologist and geomorphologist Dr. Felix Martin Hofmann of the University of Freiburg (Freiburg im Breisgau, Germany) for generously sharing his insights in a personal communication. (Learn more)
In the following blogpost, we get to know the glacial cirque lakes as landscape archives.
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A tarn is defined as a lake formed in glacially-carved cirques, often dammed by moraines.
For this enumeration of lakes in the Black Forest and the Vosges, I refer to the following work:
Woldstedt, Paul and Schwarzbach, Martin (Hrsg.). (1967): Eiszeitalter und Gegenwart: Jahrbuch der Deutschen Quartärvereinigung, Volume 18, Hohenlohe'sche Buchhandlung Ferd. Rau, Öhringen, Württemberg, p. 53 (the following tables).
The authors to a large extend lean on the following study, but supplement this information :
Fezer, Fritz (1957): Eiszeitliche Erscheinungen im nördlichen Schwarzwald, Selbstverlag der Bundesanstalt für Landeskunde
According to these sources, the northern Vosges (north-west of the Bruche Valley) contain one cirque lake (Lac de la Maix). The southern Vosges contain 12 cirque lakes (including the well-known Lac Vert and Lac Blanc). The southern Black Forest contains one cirque lake (the Feldsee on the slope of the highest mountain, the Feldberg), and the northern Black Forest contains eight such lakes (including the Mummelsee). Strictly speaking, two of the lakes in the northern Black Forest still exist only because they were dammed by humans in historical times.
×The study from which I have taken the figure attempts to reconstruct climate development during the last glacial period, between 45 000 and 22 000 years before present, based on the analysis of fossil earthworm calcite granules in loess sediments.
Fossil earthworm calcite granules are secreted by earthworms at the soil surface. They are composed of stable calcite crystals that remain chemically unchanged and preserve their structure even after being embedded in sediment. They also do not tend to migrate vertically. Therefore, they are well suited as climate proxies.
They are also ideal for radiocarbon dating because the carbon becomes decoupled from the atmosphere after secretion. From that moment on, the radiocarbon clock begins to run. The ratios of the stable oxygen isotopes ${}^{16}\mathrm{O}$ and ${}^{18}\mathrm{O}$, as well as the stable carbon isotopes ${}^{12}\mathrm{C}$ and ${}^{13}\mathrm{C}$, provide insights into temperature and mean precipitation at the time a loess layer was deposited.
Cf. Prud'homme, Charlotte and Fischer, Peter and Jöris, Olaf and Gromov, Sergey and Vinnepand, Mathias and Christine, Hatté and Vonhof, Hubert and Moine, Olivier and Vött, Andreas and Fitzsimmons, Kathryn (2022): Millennial-timescale quantitative estimates of climate dynamics in central Europe from earthworm calcite granules in loess deposits, Communications Earth and Environment, Vol 3, DOI: 10.1038/s43247-022-00595-3
×Phases of more intense glaciation are referred to as glacials, while slightly warmer periods are referred to as interglacials. Paleoclimatological evidence suggests that the Earth's climate will enter a glacial phase within several millennia in the future. Since about 2.6 million years ago (during the Pleistocene epoch of Earth’s history), glacial and interglacial phases have alternated periodically. These oscillations are triggered by periodically changing orbital parameters of the Earth, which result in periodic changes in solar insolation.
If we neglect the increase in atmospheric greenhouse gas concentrations caused by humans over recent decades, this pattern would be expected to continue in the future. However, due to global warming caused by anthropogenic greenhouse gas emissions, the Earth's climate is affected in such a way that the next glacial period is expected to be delayed by millennia or may not occur at all.
Cf. Ganopolski, A. and Winkelmann, R. and Schellnhuber, H. J. (2016): Critical insolation-CO2 relation for diagnosing past and future glacial inception, Nature, Vol. 529, 200–203. DOI: 10.1038/nature16494
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Cf. Lang, Gerhard (2005): Seen und Moore des Schwarzwaldes - als Zeugen spätglazialen und holozänen Vegetationswandels. Staatliches Museum für Naturkunde Karlsruhe, Herausgegeben von Trusch, R. und Wirth, V., Karlsruhe, Gestaltung und Druck: Guide Druck GmbH, Tübingen, p. 26
Hierin bezieht er sich unter anderem auch auf den Hydrogeographen Wilhelm Halbfaß (1856 – 1938).
×In a study from last year, Dr. Felix Martin Hofmann and his team analysed cirques in a region west of Freudenstadt (near Bad Rippoldsau). They combined high-resolution digital terrain models with their own field surveys. The high-resolution digital terrain models are based on LiDAR (Light Detection and Ranging) remote sensing technology. In this method, the surface of the Earth is scanned from an aircraft using pulsed laser light. Similar to radar technology, the time is measured that it takes for the radiation reflected by the terrain to be detected. LiDAR uses laser light in the visible spectral range. Through repeated laser pulses over a large area, a very large number of time-of-flight measurements are collected and processed into a three-dimensional model of the terrain.
Dr. Hofmann and his team were able to verify the cirques documented in the 1950s and 1960s in the study area, as well as identify previously unknown cirques.
In this study, the Teufelsries cirque was also revisited. For this cirque, Adolf Zienert and Fritz Fezer (1967), as well as Fritz Fezer (1971), concluded that it must have temporarily contained a small lake dammed by a moraine. They based their hypothesis on the presumed discovery of lake sediments ('compressed, loamy-clayey varves') with a total thickness of 1.5 to 2 m. However, Dr. Hofmann and his team were unable to verify these observations and conclusions during their own field excursion to the site in 2025 (this may partly be due to the fact that the precise location of the outcrop was not documented in the studies by Fezer and Zienert).
Cf. Hofmann, Felix Martin and Vorwerg, Leo and Witschel, Robert (2025): Refining the mapping of cirques and moraines in the central and northern Black Forest, south-west Germany, with remote sensing data and cirque metrics extraction, Journal of Geomorphology, 41-66. DOI: 10.1127/jgeomorphology/0856
The mentioned studies from Fritz Fezer (1957) and Fritz Fezer and Adolf Zienert (1967):
Zienert, Adolf, & Fezer, Fritz (1967): Vogesen- und Schwarzwald-Kare, E&G Quaternary Science Journal, 18(1), 51–75
Fezer, Fritz (1971): Zur quartären Formung des Nordschwarzwaldes, Jahresberichte und Mitteilungen des Oberrheinischen Geologischen Vereins, 53, 183–194
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The importance of toponyms is estimated by Fezer as follows:
Niches where the name of the forest compartment contains the word 'See' (lake), 'Weiher' (pond)cor 'Wasser' (water), are subsumized under group 9. As the border of the Black Forest was populated 700 A.D. and the Black Forest only after 1000 A.D., … the forest names the forest names can be at most 1300 years old. Therefore, at that time in these niches lakes still existed.
Cf. p. 21 in:
Fezer, Fritz (1957): Eiszeitliche Erscheinungen im nördlichen Schwarzwald, Selbstverlag der Bundesanstalt für Landeskunde
On the history of toponyms in the Black Forest, cf.
Jänichen, Hans (2026): Historischer Atlas von Baden-Württemberg: Beiwort zu den Karten 4, 1–2, Der alemannische und fränkische Siedlungsraum, Landesamt für Geoinformation und Landentwicklung Baden-Württemberg
It can be assumed that toponyms in the Black Forest originate from the early middle ages the earliest. Palynological studies (nest blogpost) suggest that human intervention such like deforestation happened already much earlier – in the Iron Age. These interventions might not have had a formative influence on the toponyms that are still used today. Presumably, the forest was used in these early times by small groups of humans locally. Systematic development – by farm and village foundations and conversion of forest areas into arable land, meadows, and settlement land – started with the early Medieval times.
Hans Jänichen writes:
Linguistic and written sources are sparse and appear only sporadically around 700 A.D., more frequently around 800 A.D., and then dwindle again between 900 and 1050 A.D. Therefore, toponyms – alongside burial sites – serve as the most importnant historical witnesses.
Original German text (translated by me):
Da andere sprachliche und schriftliche Quellen vereinzelt erst um 700, in größerem Maße sogar erst um 800 einsetzen und zwischen 900 und 1050 wieder weitgehend versiegen, sind die ON neben den Reihengräberfriedhöfen die wichtigsten Zeugen für die Zeiten, in denen eine schriftliche Überlieferung fehlt.
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Cf.
Hofmann, F.M. (2025): Landscape Evolution of the Black Forest: From the Variscan Orogeny to the Modern Era, in: Lehmkuhl, F., Böse, M., Krautblatter, M. (eds) Landscapes and Landforms of Germany, World Geomorphological Landscapes. Springer, Cham. https://doi.org/10.1007/978-3-031-77876-6_17
Fezer F, Günther W, Reichelt G (1961) Plateauverfirnung und Talgletscher im Nordschwarzwald. Abhandlungen der Braunschweigischen Wissenschaftlichen Gesellschaft 13:66–72
