The Detachment Physical Weathering Form Group Affecting Stone Building Materials at The Archaeological Site of Sabratha, Northwest Libya

The archaeological Sabratha City is a UNESCO World Heritage site located on the Mediterranean Sea coast west of the Capital City of Tripoli north of Libya. Like many other archaeological cities in the world, Sabratha monuments have been built using naturally existing stones which according to the rules of nature are subjected to continuous weathering processes and become damaged to varied degrees. The range of extension as well as the type of stone damage is dependent on the reacting stone materials with the natural weathering processes. From an important point of view, the preservation of stone monuments now has attained the care of the government institutions who are in concern. The present paper discusses the main physical weathering forms belonging to the weathering form group-3 "the detachment group" which has been established by (Fitzner, and Heinrichs, 2002, 2004). The methodology of this research will be based on applying certain forms invented by Fitzner and Heinrichs that serve to estimate every damage of weathering forms affecting the monuments of Sabratha City. A number of nine main weathering forms of the detachment group including about fifteen individual weathering forms were found to affect the whole monuments of the city with damage intensity degrees varied between non-visible damage and moderate damage (0 degrees and 3 degrees). To make it easy for observations, fifteen contour maps were drowning for each individual weathering form showing the damage intensity degree and distribution. To summarize the overall picture of the weathering form damages, linear and progressive damage indices were found and mapped. Diurnal and seasonal temperature variations; relative humidity fluctuations; salt crystallization; moisture and or water content are factors expected to produce such weathering damages. As a recommendation, the authorities in response are invited to take this matter seriously and should act to protect the built heritage of Sabratha City.


Introduction
Usage of natural stones for buildings and monuments may characterized the history of mankind through the live, which with the passage of time, they become affected by weathering processes.(Fiitzner andHeinrichs, 2002, 2004).Weathering can be physical, chemical or biological.Physical or mechanical weathering is the process by which a natural rock become fragmented into smaller pieces without changing in its chemical composition.While chemical weathering is the process that acting on the rock and causing chemical reactions that lead to generation of new minerals especially when become in contact with bodies of water at near surface environment.Biological weathering is the interaction between the activity of any biological sources such as plants, animals and others with the surface of different types of rocks and may damage them through secretion of acidic compounds (Pamela, 2013;Zambell et al., 2012;Uroz et al., 2009;Goudie and Viles, 2008;and Calvaruso et al., 2006).Monuments that are not maintained sufficiently or are not restored appropriately will be surely subjected to stone damage.Recently, a new techniques and research technologies were introduced to study the damage characteristics and monument restoration activities (Fiitzner andHeinrichs, 2002, 2004).In this domain, Fitzner and Heinrichs explained the principles of evaluation concerning weathering of monument stone materials.In this context, they defined the classification scheme of weathering forms (level 1: group of weathering forms, level 2: main weathering forms, level 3: individual weathering forms, level 4: intensities or parameters).Beside to these, they have also referred to the damage categories and the damage indices of the Weathering forms.In general, they defined (4) groups of weathering forms (group 1: loss of stone material divided to (3) main weathering forms and (18) individual weathering forms and (3) classes of intensities or parameters, while group 2: discoloration/deposits divided to (9) main weathering forms and (25) individual weathering forms and about ( 14) classes of intensities or parameters, while group (3) the detachment is divided to (11) main weathering forms and about (11) individual weathering forms and ( 12) classes of intensities or parameters, the last group ( 4) is the fissures/deformations which is divided to (2) main weathering forms and about (4) individual weathering forms and about (3) classes of intensities or parameters).The present research which concerning with Sabratah archaeological site will discusses only the weathering form group (3) that affects the stone building materials.The weathering form group (1): "the loss of stone material" that affects the stone building materials of Sabratah monuments has been discussed earlier (Shushan et al., 2019).

Location and Definition of the Study Area
The archaeological Sabratha City is located on the Mediterranean Sea coast about 70 km (43 miles) west of the Capital City of Tripoli north of Libya, within the coordinates: 32°47′32″N and 12°29′3″E as shown in Figure ( 1).It is bordered by the sea from north, Zawiyah City to the east, Jafara to the southeast, Yafran to the south and Zuwarah City to the west.This archaeological site become as a UNESCO World Heritage Site in 1982 (Agence France-Presse, 2017; Francois Decret, 2011;and Sha'biyat of Great Jamahiriya 2009).
Sabratha has been known as an old port city along North Africa coast which is in now days known as Libya State.The Berber Zwagha tribe were have been known to occupy Sabratha Site and gave it their name in the 8th century BCE (as noted by the historian Al-Bakari, 11 th -century CE).Sabratha became a Carthaginian Colony under the name of Tsabatan and have been a part of tri-city trade network for Greeks recognized as Emporia.The Site of Sabratha was taken by Numidians in (c.202-148 BCE) after the death of Carthage in the 2nd Punic War in (c.218-202 BCE) and it has been governed then by Masinissa' grandson Jugurtha in (r.118-105 BCE) .It was taken then by Rome after Jugurtha's death in (105 BCE) and during the reign of Julius Caesar (48-44 BCE) it became a part of Africa Nova Province (Mark, 2019).

Statement of The Research Problem and Objectives
Before the year 1911 CE, the Monuments of Sabratha Site were located under the sand as being buried due to sea and wind storm action.The city was recovered by excavation activities brought by the Italian government in 1911 CE (Mark, 2019).Sabratha Monuments were undergone dangerous periods of erosion were buildings become crumbled due to storm and unsettled sea conditions (Agence France-Presse, 2017; Francois Decret, 2011;and Sha'biyat of Great Jamahiriya 2009).The main goal of this research is to evaluate the physical weathering damages on the stone building materials of Sabratha monuments caused by weathering group (3) which is the "Detachment Group" This will include: classification of the damages of each weathering group as discussed by (Fitzner andHeinrichs, 2002 and2004) (ex.Main Weathering form, individual weathering form, weathering intensity), establishing the location and distribution of each class of weathering damages within the ancient Sabratha City, mapping of each type of weathering damage intensities that affect the stone building materials and mapping of the "linear and progressive Deterioration indices-LDI and PDI" of group (3) of weathering forms.
Methodology of this research will be based on applying certain forms invented by (Fitzner et al., 2002 and2004) that serve to estimate every damage of weathering form.This include estimation of the damage intensity percentages (%), estimation of the damage intensity categories and measurement of flakes thicknesses (mm) that detaching from the stone building materials at Sabratha monuments.

Stratigraphy of The Study Area
The area of study is surrounded from the south and south-east by a series of rock units belonging to Jabal Nafusa (Nafusa Mountain) which have been used as row materials from which stone buildings were prepared to establish the monuments of Ancient Sabratha City.The distance between Sabratha City and the Jabal Nafusa Series is about 86.19 km.The area of study is covered by rock units limited between the Late Triassic and Quaternary.The study of El Hinnawy and Cheshitev (1975)

Results and Discussion
The investigation done in the area of study concerning the evaluation of the damages caused by weathering form group (3) has followed the map shown in Figure (3).The results of weathering form group (3) "Detachment" affecting the studied monuments at Ancient Sabratha City are summarized in (Tables 1-5).
The results of the calculated damage indices (Linear and Progressive damage indices) for weathering form group-3 that effect the stone monuments at Sabratha City is represented in Table (2).In order to conclude the conclusive quantification and rating of weathering damage effect on stone monuments, the damage indices were applied.According to calculation modes effectuated by (Fitzner and Heinrichs, 2000), the damage indices may range between (0 and 5).The linear damage index (Map 16) refers to the average damage category, whereas the progressive damage index (Map 17) refers to the proportion of higher damage categories (Fitzner et al., 2000;and Heinrichs, and Fitzner, 1999).Table 2. Estimation of damage intensity percentages (%) of detachment group of weathering that affecting the stone building materials at Sabratha monuments according to damage category groups established by (Fitzner et al., 2002).

Sabratha Archaeological Sites
Group Table 3. Estimation of damage intensity of detachment weathering group that affecting the stone building materials at Sabratha monuments according to damage category groups established by (Fitzner et al., 2002).

Sabratha Archaeological Sites
Weathering  Many factors of mechanical weathering were considered to be effective to create such damages like that established on stone monuments of Sabratha City, which may include expansion and contraction of the building stone materials caused by temperature variations between day and night and from summer to winter seasons, freezing and thawing cycles can create damages to the monuments, salt crystallization can also produce damages on stone monuments, fluctuations in relative humidity can also change the overall composition of stone monuments and may damages them, the moisture content (water adsorbed by rock materials) especially clays may swell and cause damage to surrounding rock materials of stone monuments (Gore Pamela, 2013;Zambell et al., 2012;Uroz et al., 2009;Goudie, and Viles, 2008;Calvaruso et al., 2006;National geographic Society, 1996-2019).According to the results shown above, the degree of intensity range of each individual form of weathering affecting the stone building materials of Sabratha monuments are generally speaking closely similar with few exceptions in certain sites which may owing in part to the similarity in the lithology and type of stone buildings and in the other part to the type (types) of mechanical weathering agents acting in the region.As a matter of fact durable and resistant stone building materials are off course more resistible to weathering agents.Therefore, the degree of intensity range of the individual weathering forms discussed here is directly proportional to degree of resistivity and durability of the stone building materials of the monuments.We also mention that the overall original texture of stone building materials of the monuments can  2) and (Maps 16 and 17).

Conclusion
The weathering form group-3 "the Detachment Group" is a mechanical or physical weathering group has been found to effect the stone building materials at Sabratha monuments.Fifteen individual weathering forms were investigated and found to affect the overall area of study with slightly varied degrees of damage intensities ranges (varied between 0 and 3 categories).Weathering agents that act to produce damages on this group are most likely include, the diurnal and seasonal temperature variations; relative humidity fluctuations; salt crystallization; moisture and or water content and to some extent freezing and thawing cycles (when the temperature has lowered to degrees close to zero).The slight differences in the degree of damage intensities is resulted due to differences in the degree of resistivity of stone building materials to weathering agents and the overall original texture of those stones as well.

Recommendations
We recommend through this research the Libyan Tourist Agency or the authorities who are in responsibility to take action to minimize or prevent the continuous damages on the stone building materials at Sabratha monuments due to this types of weathering forms.We also recommend that all other types of weathering forms group-2 "discoloration-deposits" and group-4 "fissures-deformations" to be investigated at the Ancient Sabratha City.
made on Jabal Nafusa and the surrounding areas is used to classify and define the different rock units outcrop in the area which is summarized in the stratigraphic column shown in Figure (2).

Figure 3 .
Figure 3. Locations of the studied monuments at Ancient Sabratha City Photographs refer to Table (1).Close-up views representing 3 types of individual weathering forms belonging to "Flaking; photo1, Contour scaling; photos: 2 and 3, Granular disintegration; photo: 4" which is part of the main weathering form group-3 "Detachment".
role in accelerating the weathering process.The close similarity in the degree of intensity range of the individual weathering forms has been emphasized also through the results of the linear and progressive damage indices showed in Table( Shushan et al., 2019Faculty of Marine Resources, Alasmarya Islamic University, Libya.

Table 1 .
Presentation of results belonging to weathering form group-3 that affect stone building materials at Sabratha monuments * .

Map-16 refers to Table (1).
Distribution and intensity of the linear deterioration index belonging to weathering form group-3 that effect stone monuments at Sabratha City.
Map-17 refers to Table (1).Distribution and intensity of the progressive deterioration indexbelonging to weathering form group-3 that affect stone monuments at Sabratha City.