This assignment is for ETC5521 Assignment 1 by Team Possum comprising of Brenwin Ang and Joyce Lee.

Introduction and motivation

Volcanoes date back to hundreds and thousands of years ago where the first documented eruption occurred in Santorini back in 1650 BC! Accompanied by its mysterious image in our eyes, volcanoes touch on a wide range of knowledge, including geochemistry, petrology, seismology and more. This topic seems to be complex and distant from people like us who did not take further studies on this area. Yet we chanced upon data set released by TidyTuesday which is probably one of if not the most comprehensive data set to learn more about volcanoes. This data exploration enable us to take a closer look at the more recent active volcanoes around.

Although volcanoes are nature’s explosive land forms and yet one of the most beautiful, it is inevitable for us, as human being to neglect its impact on our lives. Based on our understanding on volcanoes, we develop two themes that will be surrounding this entire analysis, which are “severity” and “safety” so as to establish more interesting facts!

We start with a brief introduction into the world of volcanoes, then visit the interaction between volcano & humans and finally looking into the characteristics of volcano.

Data description

The data source is from The Smithsonian Institution, which has been constantly updating since 2013. The data is cleaned and made available for download on (https://github.com/rfordatascience/tidytuesday/blob/master/data/2020/2020-05-12/readme.md), so that we directly import the 5 data sets for this analysis. These 5 data sets are probably the most comprehensive data set around. They are volcano, eruptions, events, tree_rings and sulfur, allowing us to discover the influences among them.

The data source is from The Smithsonian Institution. The data is available, and cleaned, downloadable from tidytuesday github. Cleaning script is also supplied.

Data provided contains 5 linked data sets, each with looking at a particular aspect of volcano:

Research questions

Analysis and findings

World Of Active Volcanoes

World Map of Active Volcanoes erupt

There are 3 main types of Active(erupted before) Volcanoes namely Stratovolcano, Caldera and Shield. We decided to label the others as others. Stratovolcanoes are by far the most active volcano.

We first plotted the world map of Active Volcanoes with tectonic plate boundaries overlaid.

We found that most of the volcanoes lie along the Pacific Ocean tracing the boundaries of tectonic plates. We later found that was dubbed the Ring of Fire(or Circum-Pacific Belt) . This path is approximately 40,000km long and holds 75% of the World’s Volcanoes are situated and 90% of active ones! The abundance of volcanoes are explained by significant tectonic plates in the area since volcanoes are formed by either converging or diverging tectonic plate boundaries, creating cracks in earth.

To achieve the map, we could not just plot the tectonic boundaries as the polygons stretch across the world map (looking like they are at opposite ends of the world when in fact they are side by side since the globe is round while ggplot is 2D). So, we split the tectonic plates at the prime meridian (x-intercept where long = 0) - was assisted by a helpful member Z.Lin at StackOverflow. Also, we joined the datasets with world map provided by ggplot to find continent and country coordinates as well as dataset from Kaggle to obtain coordinates to plot the tectonic plates polygon.

This map zoomed into the Ring Of Fire, showing the volcanoes running along the boundaries. Relatively speaking, the volcanoes here have more eruptions.

The interaction between volcanoes and humans - How worried should you be about volcanoes?

Population around volcanoes’ vicinity

With the above visualization, the height of the triangle(volcanoes) corresponds to the number of volcanoes that are within a population category 5km, 10km, 30km and 100km from the volcano’s vicinity respectively.

Majority of the population within 5km reach of a volcano were less than 100. At a 10km range, it was a mix of population sizes. And having a population of more than 100,000 is relatively scarce.

So how far must you be from a erupting volcano to be safe? There is no fixed safety risk zones(or distance) as volcanoes are unpredictable. Generally, around 1km for small/medium sized eruptions(VEI = 1-2) is relatively safe as long as volcanic projectiles do not fall in that area.Volcanic Discovery%20Low%20Risk%20Zone&text=Typically%20you%20are%20more%20than,pyroclastic%20flows%20could%20be%20channeled.) Above figure was inspired by Sil Aarts’ visualization where we use geom_polygon to create easy and intuitive visualizations.

World map with number of eruptions in each country

Above shows plot with fill depending on the number of eruptions in each country and larger dot sizes represent the number of population in the vicinity.

Prominent countries(shaded orange) with the most active volcanoes lie on the Ring Of Fire.

How likely will a volcano erupting in each VEI category after 1812?

VEI measures the explosiveness of volcanic eruptions. It is determined by the volume of materials thrown out(e.g. pyroclastic flow like smoke, ash etc.), eruption cloud height and qualitative observations. As qualitatlively described using terms ranging from “gentle” to “mega-colossal” [Wikipedia]. For example, VEI of 0 given for non-explosive eruptions (\(<10,000m^3\) of fragmental material produced by eruption called tephra). While VEI of 8 can eject \(1\times10^12m^3\) of tephra.

Theoretically, VEI is ranges from 0 to infinity. VEI scaled is on a log scale. Therefore each interval (increase of 1 in VEI) indicate an eruption 10x more powerful. Looking back at the last 132 million years, there were only 40 eruptions documented with VEI-8 magnitude and 10 eruptions of VEI-7 in last 10,000 years.

We filtered the data set to from present to after 1812 - where the last observed VEI 7 was recorded at Mount Tambora and plotted a density plot of VEI against the number of eruptions. Under the plot represents the number of volcanoes with the corresponding number of eruptions (slightly jittered).

The density plots above shows that likelihood of a volcano with VEI 4 or above is very unlikely (less than 1). In fact, almost 98% of all volcanoes have less than VEI-3.

As for lower, VEI categories, a volcano with VEI-2 occur rather frequently with quite a number of them occurring > 50 times over the time span.

So, How Frequent does volcanoes erupt?

Tiles in above plot are used to visualize frequency with Most Active Volcano filtered in each VEI Category. Each tile represents an eruption.

Eruptions with VEI 2 occurred the most frequently, followed by volcanoes with VEI-3. For VEI-4 and above, volcanoes rarely erupted (or erupted prior to 1812) - Kelul-4 was actually an exceptional case as the other VEI-4 volcanoes occurred very seldom.

The gentler eruptions erupt more frequently while more explosive eruptions occur far less frequently.

Which tectonic settings have longer or shorter eruption duration?

The figure first orders the volcano eruptions with long duration ( >365 days) by their tectonic settings. Subduction zone / Continental crust ( >25km) dominates among all tectonic settings with most long duration eruptions both intuitively and proportionally - 90 long duration eruptions, accounting for 58.824% compared with others. Followed by Subduction zone / Continental crust ( >25 km) is Subduction zone / Oceanic crust ( <15km), yet a large gap between them is displayed. Particularly, 14 long duration eruptions occur on Subduction zone / Oceanic crust ( <15km), resulting with 9.15%. The remaining tectonic settings have very close figures, as well as proportion, having Intraplate / Intermediate crust (15-25 km) be the one with least long duration eruptions. In the same way, the number of short duration ( <30 days) eruptions for each tectonic settins is exhibited below. A similarity between this plot and the above one for long duration eruptions is that Subduction zone / Continental crust ( >25 km) and Intraplate / Intermediate crust (15-25 km) still remain in the same position, in this case - short duration eruption. Some variation emerges within the middle range of the order. For instance, there are only 7 long duration eruptions (4.575%) on Rift zone / Oceanic crust ( <15km), however the number of short duration eruptions rises to 30, accounting for 10.067% among all tectonic settings. Moreover, comparing the length of the bars, it is apparent that every number from long duration eruptions for all tectonic settings increase when it comes to short duration. Hence, short duration eruptions occur more frequently than the long ones.

World map of long and short duration eruption

The map plots the locations of the volcanoes, categorised by their duration of eruptions. It can be easily observed that volcanoes with short duration eruptions are more concentrated, so are more likely to form into a “line” shape. On the other hand volcanoes with long durations seem to be more dispersed. Looking at them as a whole, volcanoes are mainly located in coastline areas.

World map of eruption based on VEI level

This map captures the volcanoes that have erupted from year to year according to their respective VEI level.

Which tectonic settings have high or low frequency of eruptions?

The figure depicts the tectonic settings with the record of at least two or more volcano eruptions within one year. Out of 10 tectonic settings recorded (NAs excluded), only 6 of them are listed under this condition. Tectonic settings with both long and short duration eruptions have all been listed here in regards with high frequency. Subduction zone / Continental crust ( >25km) is again positioned with the most times (21 times) of eruptions of high frequency, but this time followed by Intraplate / Oceanic crust ( <15km), where only 7 high and 15 short duration eruptions are marked. Rift zone / Oceanic crust ( <15km), placing with the least eruptions of high frequency, actually has 30 times of short duration eruptions which is considered quite high.

Discussion on tectonic settings and average VEI

Grouped by 10 tectonic settings (NAs excluded), volcano eruptions on Rift zone / Intermediate crust (15-25 km) have the highest average VEI of 2.667, whereas those located on Intraplate / Oceanic crust ( <15 km) obtain the lowest average VEI of 0.923. Reflecting on one of the findings, as the tectonic setting where most longer ( >365 days) and shorter duration ( <30 days) of eruptions occur, meanwhile with most higher frequency ( ≥ 2 eruptions within 1 year) of eruptions, Subduction zone / Continental crust (>25 km) does not incur a high average VEI. It instead lies in the middle range among the 10 tectonic settings, with the average VEI of 1.982.

Overall, with the highest VEI average (2.667), neither long duration eruptions ( >365 days), nor high frequency (≥ 2 eruptions in 1 year) eruptions are found in Rift zone / Intermediate crust (15-25 km), while only one eruption of short duration ( <30 days) occurs in this setting. On the opposite, with the lowest ranking for average VEI (0.923), volcanoes on the Intraplate / Oceanic crust ( <15 km) don’t tend to erupt with long duration ( >365 days) where it’s long duration eruption only holds 4.575%, compared with other tectonic settings. Nevertheless, it has a greater percentage for both short duration (5.033%) and high frequency (9.677%) eruptions.

Average VEI level for each tectonic setting
tectonic_settings Avg vei
Rift zone / Intermediate crust (15-25 km) 2.667
Intraplate / Continental crust (>25 km) 2.250
Subduction zone / Intermediate crust (15-25 km) 2.195
Rift zone / Oceanic crust (< 15 km) 2.132
Intraplate / Intermediate crust (15-25 km) 2.091
Subduction zone / Continental crust (>25 km) 1.982
Subduction zone / Oceanic crust (< 15 km) 1.796
Rift zone / Continental crust (>25 km) 1.714
Subduction zone / Crustal thickness unknown 1.623
Intraplate / Oceanic crust (< 15 km) 0.923

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