Weathering is something I think that most of us don’t even
consider. We look at things like Roman ruins and just think “They’re old. Of
course they’re decaying.” Of course, there is always a reason for such decay,
and Roman ruins are absolutely full of it.
Pictured to the left are the remains of the Temple of Castor
and Pollux in the Roman Forum. Let’s begin by pointing out the obvious: there’s
a bit of flaking on the surface of the marble. The can be explained by a
process of mechanical weathering called “Wetting and Drying”. The marble
absorbs water (we can assume rain here) and expands, then contracts as it
dries. This causes internal stresses in the marble. After, when the marble
heats up, a “baking effect” occurs and leads to surface flaking. 
Let’s now travel into the Mamertime Prison, or the
Tullianum, and take a look into its depths. It is pictured at the right. You’ll
probably notice quickly that the walls look green. The walls look that way due
to a process called oxidation, which is a chemical weathering process. I always
thought oxidation created a red color, but consider that the walls are full of
copper, and the process makes complete sense. Copper turns green when it is
oxidized. Cool stuff, huh?
Finally, pictured below are some ruins just outside of Rome.
What stick out to me most about these ruins are the little holes in the stone.
These holes are created by salt weathering. Salt crystals form and exert
pressure, creating the little holes and general decay we see in the rock.
Image sources:
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhr1pCJQeEtLFW-HABv3xBzZDDBsMwZvKQ2xdhddDN6a3OyQGRqOYej2UHySuoIGCw1XELiK6fjzsvjsYn6Ra7agpOqvChHR0YkWs2Oq2IKCrHk40DQzP-IvR2gkgXe15gLmuFP0IL2SKTY/s400/pergeperfect.jpg
http://upload.wikimedia.org/wikipedia/commons/3/37/RomaForoRomanoTempioCastori.jpg
http://upload.wikimedia.org/wikipedia/commons/8/8f/Mamertine_Prison.jpg
Information Sources:
http://www.stonecaretechniques.com/8_m.htm
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CEEQFjAC&url=http%3A%2F%2Fstaff.harrisonburg.k12.va.us%2F~esutliff%2Fforms%2Fweathering_erosion_soils_1327072876.ppt&ei=GkZ3UK3vGenFiwKNr4DIBQ&usg=AFQjCNHiE1yJnOH7rMrFIGWvCHjj8AC5Ug&sig2=qBHowA2wBiTh9BT2NIFQnQ
