Progreso pier, Yucatán Peninsula, MexicoThe light grey structure at the centre of this photog

Progreso pier, Yucatán Peninsula, MexicoThe light grey structure at the centre of this photograph is the world’s longest pier, located off the Yucatán Peninsula in Progreso, Mexico. It measures 6.5 km (4 mi) long and was extended in 1985 from it’s original length of 2 km (1.2 mi). The purpose of this phenomenally long pier? To allow luxury cruise liners (and occasionally container ships) to dock at the small port city, which sits atop a very gradually sloping, shallow limestone shelf.There is a distinct difference between the colour of the ocean surrounding the upper half of the pier when compared with the lower: this is due to obstructed sediment erosion and accretion. In coastal beach systems, sediments are transported by longshore drift, a process where the ocean current continuously erodes and redeposits sediment, causing the beach to gradually “drift” along with the prevailing current direction (influenced by wind direction). Along the Yucután Peninsula, the current moves in a northwesterly direction. In the photo, the darker sections of ocean represent deep water, while the lighter areas represent shallow. Why is there such a difference in depth either side of the pier, as well as the top and bottom? According to research led by Gabriela García-Rubelohat, it’s likely due to the underlying support structure which forms a man-made littoral drift barrier. This leads to “updrift accretion and downdrift erosion”: the southernmost, older portion of the pier, sits atop arches which allow sediment to be transported naturally, whereas the newer portion (which straddles the darker water) was built on a solid structure, preventing sediment flow. This has resulted in the accumulation of sediment on the right side of the pier, and erosion on the left. You’ll also notice that the shallower water (i.e. sediment accretion) curves around the top of the pier, nicely illustrating the longshore drift we talked about earlier. So, is the pier having a negative effect on the area? Maybe not. Research by Paulo Salle et. al. (2013) suggests that the beaches surrounding Progresso are stable and not undergoing significant erosion or deposition. - YKReferences:García-Rubelohat et. al. (2015) http://bit.ly/1Dvh32n(requires journal access)Salle et. al. (2013) http://bit.ly/1BRSTKU (PDF)Image credit:NASA 2014 (http://1.usa.gov/1tTmvDu)Further reading:Downdrift erosion - http://bit.ly/14FDraL (available free to read on JSTOR but requires signup). Original article on NASA Earth Observatory - http://1.usa.gov/1w7aiuSVisit the pier on Google Earth - http://bit.ly/1KvieAJ -- source link

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