Walther Penck (30 August 1888 – 29 September 1923) was a geologist Penck's idea of parallel slope retreat led to revisions of Davis's cycle of erosion. He obtained a PhD by studying petrology at the Heidelberg University. Between 1912 and 1915 he worked in Dirección General de Minas in Buenos Aires before moving to the University of Constantinople where he was named professor of mineralogy and geology. He finally settled as professor in the University of Leipzig in 1918. It was characteristic of Davis to react violently and disdainfully to criticism, particularly to this German criticism; it was also his characteristic to choose to attack the most vulnerable points of that criticism. Regarding Walther Penck's objections to the Davisian geographic cycle Davis commented to Albrecht Penck in 1921:
<blockquote>It is pleasant news that your son, Walther, is established as professor in Leipzig where his father long ago studied. As he may have told you, I have enjoyed reading parts of his Argentine monograph, an able piece of work, and I have written asking him to specify the difficulties he finds in accepting the cycle theory. I am inclined to believe that he really does not know what that theory is...</blockquote>
Walther Penck died of oral cancer in September 1923.
- : A series of folds and synclines analogous to orogenic folding. It is usual type of folds created by lateral compression in the crust. As the develops it narrows at the same time they become higher. Can be translated as 'great fold' in English. Davis translated it into 'broad fold'. Penck himself was unhappy with the term .
- Piedmonttreppen: descending erosional benches on an uplifted area. Their shape is more or less concentric. Penck interpreted the as the result of doming. Benches he thought originated as in the periphery of the dome before they were uplifted. In Penck's valley development model the steepness of valley slopes depended on the rate of uplift; this view contrasts with the Davis's erosion cycle, in which valley slope steepness depends on its relative age or stage of development.
Landform associations
225px|thumb|[[Sierra de Famatina in Argentina interpreted as part of a by Penck. criticized the theories Walther Penck outlined in . Geographer Martin Simons claimed in 1962 that Davis misunderstood and mis-translated parts of the paper leaving a distorted view of Penck's ideas among later workers. Simons therefore does not consider Davis an adequate critic of Penck's work. Other factors detrimental to an understanding of Penck's ideas include his early death and his confusing writing style. Douglas Wilson Johnson, a coastal geomorphologist and staunch supporter of Davis, criticized Penck's theory harshly as:
:"Penck’s conception that slope profiles are convex, plane, or concave according to the circumstances of the uplifting action, [as] one of the most fantastic errors ever introduced into geomorphology"
Penck's theories had a much more limited influence in Germany compared to the English-speaking world where they gained notoriety for their contrasts to Davis'.
Geographer Allaoua Saadi remarks by 2013 that Penck's and Davis' ideas have become more compatible and even complementary since the advent of modern tectonic theory. This author claims that Davis' ideas are more applicable near active margins where tectonics are "cataclysmic" and Penck's ideas fit better in passive margins and continental platforms.
Walther Penck has a volcano named after him in northwestern Argentina.