Before and After LANDSAT imagery on the 1991 Mount Pinatubo Eruption in the Philippines by Anna Canto

This is a short discussion I wrote for my GSCI100 - Intro to Geospatial Tech class regarding Earthshots (See link below), a series of satellite images that have helped monitor the ever-changing earth.

The LANDSAT program is a joint NASA/USGS program that provides the longest continuous space-based record of Earth’s land in existence [1]. It is a great program wherein it provides essential information daily that aids land managers and policy makers in making wise decisions about our resources and our environment. My example is one of the many reasons why I believe remote sensing is quite essential and beneficial to everyone.

The example I chose is a well-known volcano for both foreign and local geologists due to it being the world's largest volcanic blast since the Alaska's Novarupta in 1912. When Mount Pinatubo erupted, the volcanic ash cloud circled the world and dropped the world temperatures by ~1 degree F (or about 0.6 C) for about two years [2]. It may not seem much for us but a lot of the world's ecosystems were affected by this global cooling. 

Figure 1. The images above were acquired by the Stratospheric Aerosol and Gas Experiment II (SAGE II) flying aboard NASA’s Earth Radiation Budget Satellite (ERBS). These are false-color images and they represent aerosol optical depth in the stratosphere during four different time spans. It ranges from before the June 1991 Pinatubo eruption to two years after the event. The legend shows the highest values as red pixels while lowest values are represented as dark blue. These are are normally observed in the stratosphere. See that the volcanic plume virtually covered the entire globe gradually. This is why there was a global-scale impact on the climate [2].

Mount Pinatubo is located in northwestern Luzon, Philippines (See Figure 2). Note the little green knob where Mount Pinatubo is followed by two other green knobs below it. This is a good reference for Figure 3 which will show LANDSAT imagery.

Figure 2. This is a referential map to show the approximate location of Mt. Pinatubo. This was taken from the earth shots website [3].

Figure 3. This is a LANDSAT 5 image (path/row 116/50) taken on February 18, 1989 which shows Mount Pinatubo, Philippines on the far upper left corner. Take note of the radial pattern of the meandering rivers (very light bluish to pinkish purple lines) [3]. This is prior to the 1991 eruption.

Figure 4. July 2, 1991 Landsat 5 (path/row 116/50) --- Note the volcanic plume (tufts of cloud) and the surrounding area (upper left corner) has turned brown from what used to be green.

Figure 5. Jan. 26, 1992, Landsat 5 (path/row 116/50) --- This shows that a big crater was made during the eruption and is now filled with water. Note that vegetation barely returned and the rivers were flooded with pyroclastic and/or lahar flow deposits as indicated by the pink/brown color that appear to radiate from the crater. See the extent of the tephra/pyroclastic deposits.

Figure 6. Feb. 13, 1993, Landsat 5 (path/row 116/50) --- Vegetation is reappearing at the edges of the pyroclastic deposits. 

Figure 7. January 7, 2020, Landsat 8 (path/row 116/50) --- Note that the pyroclastic deposits are hardly visible and have been covered up by vegetation. Do take note that they have been eroded away into the nearby meandering rivers if you notice the pinkish hues on the rivers.

These were acquired using an open data satellite, LANDSAT. Note the geomorphological (landform) changes recorded via the LANDSAT images from Figures 3 thru 7. It is easier to see these changes using satellite imagery that is taken periodically. This is an example of a more cost-efficient way to monitor changes in the land especially when you are studying geomorphology and the environmental changes. Different sensors (Landsat 5 thru 8) may have been used but the flight (indicated by path/row 116/50) path is the same therefore the acquired images look almost identical except for a few minor details. Spatial resolution varies for different bands but most of these images are likely to be medium resolution (~30m/pixel).

As a geologist, I enjoy looking at satellite imagery like these. I am very fascinated by how remote sensing and geographic information science is tied to my love for rocks and science. This discussion piqued my interest to manipulate the image (e.g. playing with different bands, etc) to show different interesting features. I will likely play around with these when I have more time. I love how these are free images from USGS and that there is quite a lot available for simple studies even in the Philippines. It is really useful that the resolution is just enough to note major rivers, craters (old and new) affected by this event. Last I recall, I didn't have access to such beautiful LANDSAT images when I needed it for a project I did when I worked as a university research associate. So, thank you USGS for providing these amazing earth shots! ;)

Reference:

[1] Landsat Science (n.d.) [Landsat Program] landsat.gsfc.nasa.gov. Retrieved February 28, 2021, https://landsat.gsfc.nasa.gov/

[2] Earth Observatory (June 15, 2001) [Global Effects of Mount Pinatubo] earthobservatory.nasa.gov. Retrieved January 28, 2021, https://earthobservatory.nasa.gov/images/1510/global-effects-of-mount-pinatubo#:~:text=(%E2%80%9CAerosol%20optical%20depth%E2%80%9D%20is,F%20(0.6%20degrees%20C).

[3] Earth Resource Observation and Science Center (n.d.) [Mount Pinatubo, Philippines] eros.usgs.gov. Retrieved February 28, 2021, https://eros.usgs.gov/image-gallery/earthshot/mount-pinatubo-philippines