Huge volcanoes, deep canyons, fractured ground – the Tharsis volcanic province that was covered here by HRSC in a wide swath is among the geologically most interesting and also most investigated regions on Mars. The image recorded by HRSC cuts across Tharsis from the northwest to the southeast: from the north polar ice cap in the lower left corner of the image over the giant volcanoes Alba Mons, a part of Olympus Mons, Ascraeus and Pavonis Mons that emerge over the cloud cover as darker spots, and finally the web-like Noctis Labyrinthus and the Valles Marineris canyon system with its characteristic dark-colored deposits in the upper left. A pale blue atmospheric haze marks the upper horizon which is situated near the equator.

Tharsis is a former volcanically and tectonically active region near the Martian equator covering one quarter of the surface of Mars and hosting most of the gigantic Martian volcanoes. This region rises 10 kilometers above the Martian datum, a reference that defines zero absolute altitude since there is no sea level on Mars. Tharsis volcanism is related to multiple volcanic centers of which the oldest one is situated in the Thaumasia region of the southern highlands (visible in the upper right corner of the image). Other, later active volcanic centers are situated in Syria Planum, at Pavonis and Alba Mons. A number of radiating and circumferential dike swarms in the Tharsis region can be traced back to these volcanic centers.

The development of different volcanic centers in Tharsis required a feeding source for the magma, which might have been a single mantle plume or multiple plumes possibly migrating over time. Mantle plumes are mushroom-like bodies of molten rock within the viscous Martian mantle which have a higher temperature and a lower density compared to the surrounding material, rising up to below the upper, elastic layer of the planet, the lithosphere. Such a hot, upwelling mantle can create intrusions, magma chambers and large igneous provinces.

In the upper left of the image one can find the Valles Marineris canyon system whose origin and development is closely related to the Tharsis volcanic province. Dynamic models show that the emplacement of the Tharsis rise onto the crustal dichotomy boundary, which is a topographic step separating the northern lowlands from the southern highlands, led to tension and crustal rupture at the present-day location of Valles Marineris. As a consequence, intrusives of molten rock filled the fissures created by the crustal rupture, and formed so called dikes which acted to destabilize and decouple the crustal blocks from each other. Subsidence of the blocks then created troughs and canyons that later grew in width by the collapse of wall material. The web-like pattern of troughs in Noctis Labyrinthus at the western end of Valles Marineris can be explained by interacting stress patterns.

What is special about the color image of Mars shown here is that it pictures the upper as well as the lower horizon in a global view. This image is one out of more than 1000 HRSC views and movies that have been released by ESA, DLR and FU Berlin since the start of the Mars Express mission on 2^nd June 2003. During the last 15 years the HRSC instrument has done an incredible good job in obtaining images of our neighbor planet Mars in all its facets. Even now, after more than 18,000 orbits around Mars, HRSC is still reliably transmitting data to Earth that extends our knowledge of the Red Planet.