**5. Results**

### *5.1. Endmember Groups*

The approximate locations of the 15 endmembers selected are shown in Figure 5a. SMACC first finds the brightest spectral in the image and defines it as the first endmember. In this study, the first endmember (endmember 1) represented saturated hot material. We grouped these 15 endmembers into six groups; (1) basalt; (2) hot material; (3) oxidized surface; (4) sulfate mineral; (5) water; and (6) noise (Figure 5b–g). These groups were based on the similar shape of the endmembers with the USGS spectral library; however, the amplitude of the endmembers within a group vary due to illumination conditions, spectral variability, and topography. We added up the abundances within the group to derive the abundance according to this endmembers group.

**Figure 5.** *Cont.*

**Figure 5.** (**a**) The spatial distribution of 15 endmembers extracted by SMACC; The numbers on the image indicate the approximate location of the pixels selected as the represented endmembers of (**b**) basalt; (**c**) hot material; (**d**) oxidized surface; (**e**) sulfate mineral; (**f**) water; and (**g**) noise, extracted by SMACC.

#### *5.2. Basalt Abundance*

Figure 6a indicates the presence of the dominant basalt abundance pixel throughout the image. This abundance is associated with endmember 8 which is characterized by very low reflectance (Figure 5b) due to the presence of large amounts of dark mafic rock since the study area is dominated by basaltic lava (Figure 6b).

**Figure 6.** (**a**) The abundance map for basalt endmember, yellow areas indicate the highest fraction of basalt meanwhile the black areas indicate the lowest fraction of basalt (the red box shows the approximate location of the field photo); (**b**) field photograph of basaltic lava field of the Holuhraun.

#### *5.3. Hot Material Abundance*

As shown in Figure 7a, the hot material abundance map is very sparse. This abundance is described as blends of the endmember 1, 4, 5, and 13 which are characterized by very high reflectance in the SWIR due to the presence of hot material (Figure 5c). Figure 5a shows that endmembers 1, 4, 5, and 13 are located in the lower right corner and the upper part of the image, Figure 7b shows a false color (NIR-SWIR) image which agrees with the abundance map, i.e., some patches of hot material (red-yellow color) exist in the area. The false color image is created by stacking R: 2200 nm; G: 1600 nm, and B: 896 nm. This indicates that the lava field is still emitting hot material during the data acquisition.

**Figure 7.** (**a**) Abundance map for the hot material endmember, yellow areas indicate the highest fraction of hot material meanwhile the black areas indicate the lowest fraction of incandescent lava; (**b**) The false color (NIR-SWIR) image show that hot material (red-yellow color) exists in the area.
