On patrol over France near the Swiss border, his biplane was severely damaged by machine-gun fire from four enemy aircraft.
At the end of WW I, Cloos was released from internment in Switzerland and began the study of biology at the University of Freiburg.
[3] At Breslau, Ernst met a classmate, Robert Balk (1899–1955),[4] who became a lifelong friend of the Cloos brothers and later became a professor of geology in the USA.
Ernst Cloos worked as exploration seismologist for Ludger Mintrop's Seismos company on the Gulf Coast of Texas and Louisiana and later in the deserts of Iraq.
[3][5] In 1930 Ernst Cloos received a research grant from the German government to apply the methods of granite tectonics in the Sierra Nevada.
In 1931 he received a teaching position as a lecturer at Johns Hopkins University, where he began to work on the geology of the Appalachian Mountains in Maryland.
Cloos also learned petrographic methods that had been established at Johns Hopkins University since the professorship there of George Huntington Williams (1856–1894).
From 1951 to 1954 he chaired the Geology and Geography Division of the National Research Council — during those years he spent almost every Friday in Washington, DC.