The Phlegra Montes are a system of eroded Hesperian–Noachian-aged massifs and knobby terrain in the mid-latitudes of the northern lowlands of Mars, extending northwards from the Elysium Rise towards Vastitas Borealis for nearly 1,400 km (870 mi).

The mountain ranges were first mapped against imagery taken during NASA's Viking program in the 1970s, and the area is thought to have been uplifted due to regional-scale compressive stresses caused by the contemporary formations of the Elysium and Tharsis volcanic provinces.

The presence of ring mold craters imply that significant stores of water ice may continue to persist in these terrains.

In the Phlegra Montes, some of these graben have been interpreted to host glaciers that have since given way to flow-like landforms called lineated valley fills (LVF).

[7] The core of the Phlegra Montes is a series of sinuous massifs that are interpreted to be of Hesperian–Noachian age, a greatly degraded remnant of a northern section of the southern Martian highlands terrain.

[3] Upon an initial review of Mariner 9 imagery in the 1980s, the Phlegra Montes were once proposed to be the only mountain range system on Mars strictly controlled by tectonics, although later examples of extremely linear ridges were later identified within the Claritas Fossae and the Thaumasia Highlands.

[2] A glacial interpretation for the source of the Phlegra Montes' geomorphological features requires basal melting at proportions that cannot be explained by the glacier's thickness alone.

[2] In 1970, Wolfgang E. Elston published a geomorphic map of the Cebrenia quadrangle, which stretches across wide swaths of the Vastitas Borealis Formation and the mid-latitudinal northern lowlands north of the Elysium Rise and the outflow channels to the west of the volcanic province (such as Hrad Valles).

[4] In 1976, Daniel H. Scott and Michael H. Carr published a global geomorphic map of Mars through the United States Geological Survey at a very coarse 1:25M scale.

The Phlegra Montes was noted in particular by Squyres as a site in the northern lowlands where these features were concentrated outside zones of fretted terrain.

[9] In 1985, James H. Moore of Arizona State University published an abstract for the 16th Lunar and Planetary Science Conference (held in The Woodlands, Texas) proffering interpretations of the Phlegra Montes' origin based on topographic and gravity data.

[3] In 1986, J. Lynn Hall, Sean C. Solomon (Massachusetts Institute of Technology) and James W. Head (Brown University) modeled stresses in the Elysium Rise based on the distribution of extensional and compressional tectonic features seen on Viking imagery.

Similar parallel compressional features were observed in the vicinity of the Phlegra Montes, and the authors proposed that this region may also be a fold and thrust belt.

[12] In 1995, Michael J. Pruis and Kenneth L. Tanaka of the United States Geological Survey published an abstract for the 26th Lunar and Planetary Science Conference, identifying tectonic features in the Martian northern plains that were inconsistent with a plate tectonics-based model introduced in 1994 by Norman J.

The researchers interpret that this situation could only have been possible if a period of thick kilometer-scale glaciation persisted in the Phlegra Montes, and they associate the formation of the flow with the recession of this glacier.

SHARAD radar data was used to identify the dielectric constant and the subsurface structure of the lobate debris aprons to the west of the Phlegra massifs.

[8] In 2014, German researchers Stephan van Gasselt, Julia Schulz, and Csilla Orgel (Free University of Berlin) submitted abstracts to the European Geosciences Union General Assembly meeting in Vienna and the European Planetary Science Congress in Cascais, Portugal, tied to their work mapping the spatial distribution of and updating crater age dates on lobate debris aprons in the Phlegra Montes region.

The motivation of this work is to identify obliquity-driven climatic shifts, which control the accumulation of ice-rich materials at higher latitudes.

Such landforms are abundant on Earth and are typically indicative of warm and wet climatic conditions known to have been absent on Mars in the late Amazonian period.

[2] Also in 2015, an abstract was submitted to the 46th Lunar and Planetary Sciences Conference by German researchers Stephan van Gasselt, Csilla Orgel, Julia Schulz (Free University of Berlin), and Angelo Pio Rossi (Jacobs University Bremen) regarding an updated assessment of crater count age dates in the Phlegra Montes region.

[17] In 2018, Christian Klimczak (University of Georgia), Corbin L. Kling, and Paul K. Byrne (North Carolina State University) reported a comparative assessment of eight different regions on Mars thought to have been formed through the activity of large and extensive thrust faults, comparing them to terrestrial thrust belts and certain compressive features observed on Mercury.