Impact of Environmental Factors on the Spectral Characteristics of Lava Surfaces: Field Spectrometry of Basaltic Lava Flows on Tenerife, Canary Islands, Spain

Abstract

Abstract:We report on spectral reflectance measurements of basaltic lava flows on Tenerife Island, Spain. Lava flow surfaces of different ages, surface roughness and elevations were systematically measured using a field spectroradiometer operating in the range of 350-2500 nm. Surface roughness, oxidation and lichen coverage were documented at each measured site. Spectral properties vary with age and morphology of lava. Pre-historical lavas with no biological coverage show a prominent increase in spectral reflectance in the 400-760 nm range and a decrease in the 2140-2210 nm range. Pāhoehoe surfaces have higher reflectance values than 'a'ā ones and attain a maximum reflectance at wavelengths < 760 nm. Lichen-covered lavas are characterized by multiple lichen-related absorption and reflection features. We demonstrate that oxidation and lichen growth are two major factors controlling spectra of Tenerife lava surfaces and, therefore, propose an oxidation index and a lichen index to quantify surface alterations of lava flows: (1) the oxidation index is based on the increase of the slope of the spectral profile from blue to red as the field-observed oxidation level strengthens; and (2) the lichen index is based on the spectral reflectance in the 1660-1725 nm range, which proves to be highly correlated with lichen coverage documented in the field. The two spectral indices are applied to Landsat ETM+ and Hyperion imagery of the study area for mapping oxidation and lichen coverage on lava surfaces, respectively. Hyperion is shown to be capable of discriminating different volcanic surfaces, i.e., tephra vs. lava and oxidized lava vs. lichen-covered lava. Our study highlights the value of field spectroscopic measurements to aid interpretation of lava flow characterization using satellite images and of the effects of environmental factors on lava surface evolution over time, and, therefore, has the potential to contribute to the mapping as well as dating of lava surfaces.

Testing random forest classification for identifying lava flows and mapping age groups on a single Landsat 8 image

“…However, the reference data-which is a good lava flow map produced by Smets et al (2010) in our study-does not need to be a complete lava flow map to provide training and validation samples. It is noted that this study does not intend to focus on dating lava flows through remote sensing image classification while how spectral information of lava flows can be 25 used to assess the age of lava flows is presented in other complementary articles (Li et al, 2015a(Li et al, , 2015b(Li et al, , 2017).…”

“…Pixels constituting a mixture of lava flow and vegetation or a mixture of other lava flows of different age are indeed more likely to be misclassified. In addition, spectral heterogeneity exists among pixels that are part of single lava flows: the local environment will control the weathering and vegetation evolution of a lava surface which may differ along a single lava flow (Li et al, 2015a(Li et al, , 2015b.…”

Dating lava flows of tropical volcanoes by means of spatial modeling of vegetation recovery

“…Spectral signals of lava surfaces, which indicates the change in reflectance of lava surfaces at different wavelengths, are complex and dependent on several factors and processes (e.g. Rothery and Lefebvre, 1985;Li et al, 2015b), some of which change over time and can provide estimation of lava surface age. In (semi-)arid environments, chemical weathering affects the reflectance of lava with increasing impact over time (Abrams et al, 1991;Kahle et al, 1988;Li et al, 2015a;Rothery and Lefebvre, 1985).…”

“…In (semi-)arid environments, chemical weathering affects the reflectance of lava with increasing impact over time (Abrams et al, 1991;Kahle et al, 1988;Li et al, 2015a;Rothery and Lefebvre, 1985). In more humid climates, the growth of lichens first alters the shapes of lava spectra (Li et al, 2015b;Stretch and Viles, 2002). Then, following the pioneer species, vegetation also emerges on lava surfaces, increasing the reflectance of the surfaces in the near infrared band (Head et al, 2013;Li et al, 2015a).…”

“…In mountainous terrains, elevation is closely correlated with temperature and rainfall (Aplet et al, 1998;Aplet and Vitousek, 1994;Daly et al, 1994;Li et al, 2015b;Pórtoles et al, 2011). Examples include Mauna Loa volcano, Hawai'i (USA), where more rapid vegetation succession is observed at lower elevations (Aplet and Vitousek, 1994), and Mt Cameroon (Cameroon), where a negative correlation between NDVI (Normalized Difference Vegetation Index; see definition later) and elevation range was identified (Bonne, 2006).…”