GIS Enhances Lava Flow Mapping

The current years have reflected upon the process of extensive progression in the fields of both the Geographic Information Systems (GIS) and remote sensing and such progression has contributed to the development of the mapping of the flows of lava as well as the associated study mechanism through which hitherto unavailable details could be accessed and understood as well regarding the nature and dimensions of the lava flows. The introduction and utilisation of the GIS technique, which has been composite in nature, have been associated with the attempt to obtain the optimised extents of resolution of the boundaries of the fields of lava flow. This specific technique could be identified to be associated with the dataset derived from the LANDSAT 8. The technique is also reflective of the automation of classification of various methods which are utilised to properly measure and then translate the derived information into depiction of lava flow maps. The aim of this research is to perform unsupervised classification of lava flows in Harrat Lunayyir, western Saudi Arabia, using remote sensing. The utilisation of ISODATA algorithms has been a specific element of classification. This technique is capable to enable the user to specify the number of classes the data is separated into for clustering within each land cover. The paper would as well be studying the various spectral behavioural aspects 'TOA" The goal is to characterize recent lava flows, and old lava flows based on their spectral reflectance properties. To validate the classification, we obtained samples from the same website were the ISODATA classification results have been obtained. The sample was provided to the Oregon State University for the objective of 40Ar-39Ar based determination of the age of incremental heating structures. The results are indicative of the most extensive value of reflectance wich could be obtained from those of the old lava flows. This could be explained from the perspective of the existence of considerable weathering of the observed geological formations at 800-1600 nm with the rate of 12%. The outcomes of the ISODATA based classification have been examined to be similar to that of the TOA Reflectance. The analysis of the samples could be effectively compared with that of the outcomes derived from the TOA Reflectance and ISODATA based classification. These could be presented in the following form: 15.1 ± 6.1 ka (4%) , 15.0 ± 8.4 ka (6%), 14.6 ± 23.1 ka (10%).

This paper would be reflective of the conduct of classification of flows of lava at HarratLunayyir in Western Saudi Arabia. The classification would be performed in the unsupervised manner through the utilisation of remote sensing data with the application of ISODATA algorithms. This technique is effective in enabling the researchers to outline the number of different classifications in which the data obtained could be categorised. The purpose is to form data clusters within each of the coverage of land. The study of the behaviours of spectrums being emitted from various volcanic regions, which is known the 'TOA Reflectance', as well, has been performed. The objective in this regard is to consistently outline the various categories and characteristics of both recent and old flows of lava through the evaluation of the properties of spectral reflectance. The responsibility of validation of such classification has been performed through the sampling which involved the results of the ISODATA classification.The sample was provided to the Oregon State University for the objective of 40Ar-39Ar based determination of the age of incremental heating structures.

On the (Fig.9) the common features of their reflectance spectra are illustrated based on the shape of their spectral curves. A noticeable sharp increase in reflectance from 400–500 nm for all lava classes with reflectance percentage of 12% has been observed while the maximum shifts have been identified regarding shorter wavelengths for lava flow 2, 3, 4. The steepest part of the reflectance curves in the visible blue band area of the observable range spectrum is located at 452 nm. The reflectance curves are very flat for lava flow1 and lava flow 2 except for a noticeable decrease in reflectance after 1900 nm onwards. But graduate sustained decrease for lava flow 3 and lava flow 4 after visible range.When comparing lava flows of different ages, we observed that for lava flow lava flow 1 there is a higher reflectance at 800-1600 nm at a sustained rate of around 12%. Similar sustained trend can be seen for lava flow 2 but at a slightly reduced reflectance of around 9 to 10%.

The Iso Cluster algorithm has been utilised as well and this is also identifiable as ISODATA (Iterative Self-Organized Data Analysis Techniques A) with a present classifications number of 30. Then it has been subjected to manual reclassification to an unit of 10, because at this point, the image is difficult to interpret. Decisions need to be made concerning which land cover types each category falls within. To make these decisions, other material and knowledge of the area are useful. Ground truthing could be considered to be the eventuality concerning what could be seen in the digital image with what was actually present at the time the image was recorded. This method makes this task more efficient and more accurate. The user must have knowledge of the area being classified when the groupings of pixels with common characteristics which are being produced by the computer have to be related to actual features on the ground.

In the TOA Reflectance (Fig.8, 9) one could observe the lava with the most limited geological years of age in a clear manner. It was utilised as a key to classify the lava and to choose the number of classes. We have examined different numbers of classes but we found that the best number that gave us the cluster of youngest lava has been number 10 because when you look to (Fig.10.10) the result of the classification could be found to be the same with that of the TOA Reflectance. We modified the classification process to give the oldest eruption "class 1" sequentially with the rest of the classes (Fig. 10).

In this paper we sampled (Fig. 11) from the same website where from the ISODATA classification results could be obtained (class 10-9-8) (Fig, 10) and we have analyzed the three youngest flows at Oregon State University in the Ar-laboratory. The results are: P1: plateau age 15.1 ± 6.1 ka (2 s.d. error); inverse isochron age 40.1 ± 18.8 ka (Fig.13.a). which represent Qm5, historic to late prehistoric lava flows and scoria cones. The subunit of the products is comprised by four eruption sites with black scoria cones with lava flows with surrounding with mantles of black fall ash still covering adjacent steep hillsides often similar to Precambrian basements and these could be observed to stand through the lava field. One of these sites is believed to have erupted in the 10th Century; about 1000 years ago (Al-Amri et al., 2012). P2: plateau age 15.0 ± 8.4 ka (2 s.d. error); inverse isochron age 15.1 ± 7.9 ka (Fig.13.b). It is Qm4, prehistoric lava flows and scoria cones having experienced erosion and have dust ponds of 3 m in diameter. Very black color on aerial photographs and satellite image. P3: plateau age 14.6 ± 23.1 ka (2 s.d. error); inverse isochron age 11.1 ± 5.9 ka (Fig.13.c), Qm3: Non-eroded lava flows, slight gulling on scoria cones, dust ponds up to 100 m in diameter, Qm2: Eroded lava flows and scoria cones, surface structures on flows such as flow ridges being intact with erosional rivulets in existence. Scoria cones have distinct gullies and dust ponds which could be up to 400m in diameter. These are all very young — slightly older than Holocene — and quite similar, although the analytical errors allow for age differences of 5-10 ka. In other words, P3 could be ~5 ka older than P2 which could be ~5 ka older than P1. But, overall, the measured ages indicate volcanic activity in the period 10-20 ka.

The main aim of this paper has been to conduct the unsupervised classification of lava flows in Harrat Lunayyir at western Saudi Arabia. The accurate dating of lava flows is important if we are to understand the eruptive nature of volcanoes. There are many technical details to be worked out in terms of coming up with a way to date flows absolutely using satellite techniques. We have used numerical classification methods for identifying the number of classes in which the data is separated into for clustering within each land cover.

The utilisation of ISODATA for the segmentation of the images of Landsat 8 has been also attempted. The incorporation of spatial information from the segmentation in the classifier produces a classification map regarding the homogeneous regions. The algorithm for performing unsupervised classification could be obtained from the GIS package raster (ARC/INFO). The characteristics of spectral superficiality regarding volcanic materials which could be widely observed at the zone of analysis at Harrat Lunayyir have been consistently investigated and the resultant classifications of the examined region have been spectrally. The data had been derived through the analysis involving the counting of the pixels of randomly selected regions. This could lead to the suggestion that the most elevated measures of reflectance value could be exhibited by the older flows of lava. The reason could be identified as the weathering of the same within the 800-1600 nm with the rate of 12%. On the contrary, the lava flow, which is considerably younger in geological age, has been analysed to have contained a reflectance measure of lesser intensity and the rate has been that of 9 to 10%.