Venetz

The Swiss engineer Ignaz Venetz (1788-1859) was commissioned to complete a study of glaciers in response to concerns about changing climate and glacier fluctuations on the economy of the Valais region of southern Switzerland in the wake of the Val de Bagnes disaster (1818). In the background of his portrait we see the ice dam of the Gietroz Glacier that ultimately caused the disaster: however his study was more wide-ranging in its scope. He completed his study for the Societe Helvetique in 1821, but it was not published until 1833.

On the GoogleEarth view view you can see recent ridges on the higher mountain slopes next to the glaciers and tree-covered ridges on the lower slopes next to the villages. Venetz took these lower "moraine ridges" to be evidence of glacier fluctuations.

Left: Venetz's map of "moraine ridges" in the vicinity of Simplon (shown as it appears today on the GoogleEarth view): "In the area of Simplon the moraines demonstrate that the glaciers were once much more extensive. Nothing but ice could have formed these moraines (not rockfall). Some of these moraines have been destroyed by floods, and probably many have been lost and along with them the evidence of the former size of the glaciers" (Venetz, 1833).

From this evidence together with recent historical knowledge of recent extension and retreat of ice, Venetz concluded that "the temperature rises and falls periodically, but in an irregular fashion." His attention was drawn to more distant moraines covered by forest by Jean-Pierre Perraudin (1767-1858), a local guide and hunter who reported to him that "I found at least as far as Champsec . . . these same traces which the glaciers are uncovering now." Venetz believed that these dated from "an époque that is lost in the mists of time." [Champsec is several miles down valley from existing glaciers in the Val des Bagnes]

Venetz later (1829) included farther-flung erratics as evidence of glaciation: a summary of the lecture he gave reported that “He attributes to glaciers that have disappeared, those scattered blocks and rolled stones which are widely found in different places and which are exactly like those found near existing glaciers.” His ideas were taken up by Jean de Charpentier (1786-1855) and more widely publicized in the mid 1830s.

Charpentier met Jean Pierre Perraudin by chance when lodging at his house in Lourtier in the Val de Bagnes in 1815. Perraudin told him that a great glacier must have scattered the great blocks of stones at least as far as Martigny, but Charpentier did not accept this at this time. A few years later, Venetz met Perraudin during his investigations (above). Both Venetz and Charpentier later gave Perraudin credit for his ideas. In fact several other naturalists had earlier discovered and quoted such local knowledge from among the local population, including Martel and Kuhn (see "Early Ideas" Episode): Perraudin was not unique in this regard.

“Observations made by a country fellow
from Lourtier [1818].

Having long observed marks
or^# scars made on solid, unweathered rocks, which I did not know the cause of, after much reflection I have finally, having closely observed the glaciers, judged that they were made by the pressure or weight of these same masses, whose marks I found at least as far as Champsec. This makes me believe that in the past great glaciers filled the entire Vallee de Baigne and I offer as proof to the curious by way of evidence these same traces which the glaciers are now uncovering.

Signed Jean Pierre Perraudin

# these are
all in the direction
of the valleys”

"I found at least as far as Champsec . . .
these same traces which the glaciers are uncovering now."

A REPORT ON VENETZ’S 1829 PAPER: Notice sur la 15^e Session Societe Helvetique des Sciences Naturelles, reunie a l’hospice de Grand St-Bernard, les 21,22 et 23 Juillet 1829. Bulletin des Sciences Naturelles et de Geologie (Paris) v.18 (1829) p.256 http://books.google.com/books?id=npYQAAAAIAAJ&pg=PA356

Venetz, I. 1833 (1821) Mémoire sur les variations de la température dans les Alpes de la Suisse. Par M. VeÎvetz,, ingénieur en chef du canton du Valais. Rédigé en 1821. [Memoir on the variations in temperature in the Swiss Alps. Written 1821] Denkschriften der allgemeinen Schweizerischen Gesellschaft für die gesaminten Naturwissenschaften (Memoires of the Swiss [Helvetic] Society for the Natural Sciences) v.1(2) p.1-38 http://www.google.com/books?id=cLoEAAAAQAAJ&pg=RA1-PA1