Easter Island and its underlying volcanism

BY JASON KAMMERDIENER

Modern Day Volcanic Hazards

The Following Maps and Descriptions Are For a Class Project and Are in No Way Official, Professional or Conclusive

       To draw a hazards map for Easter Island may seem a little silly as there is no indication that it has been volcanically active at any point during its inhabitation by humans.  Efforts at dating activity indicate, however, that activity originating from Terevaka and its parasitic vents in the island’s north could have taken place as recently as 2,000 years ago.¹²  As volcanologists in the USGS typically determine whether a volcano is a threat based upon whether it was active during the Holocene period (the past 10,000 years), Terevaka can still be considered a potentially active threat to the island (older Poike and Rano Kau are too old to be considered threats on this scale).¹⁴

       With no written accounts or observations of activity at Easter Island one must turn to the geological record of the island and observations of the terrain to estimate what sort of threats activity could pose.  An island hot spot like Hawaii, Easter Island’s activity would likely be characterized by low viscosity, effusive eruptions; the kind that are more dangerous to property than people (people can typically ‘outrun’ a slow moving lava flow).  Terevaka, in fact, is credited with tying the three major volcanic features of modern day Easter Island together with such lava flows.^{10, pg. 218}

       On this map the highest threat of lava flows is represented by the red and yellow areas.  They are arranged in this two-winged fashion because the features of the island indicate that there are two prominent fissures extending from the main vent at the summit of Terevaka.  Along these fissures are located the majority of Terevaka’s parasitic vents.¹⁵  The red indicates a threat in addition to lava flows unique to the areas in the immediate vicinity of the vents.  Because there are formations around the island such as Rano Raruku which are made of such materials as tuff and even rhyolite, there is clearly potential for an eruption to have enough explosiveness to throw tephra a short distance.  Baker writes that such tephra likely played a role in the formation of Terevaka’s main summit.¹²  Red areas are those areas that one is most likely to find vents with the threat of such projectiles.

       The purple area indicates a slightly lower threat of lava flow than red and yellow.  Though the purple area is located directly on the northern flank of the main summit, I designated it a lower threat because activity is likely to be focused on the two fissures rather than the main summit.  Because Terevaka has grown so tall (in comparison to the rest of the island), rising magma is likely to find an easier path out of the ground via the fissures than it would by climbing the extra distance to Terevaka’s summit.¹⁵

       Finally, the green area is the lowest threat level for lava flows.  The layout of the land seems to indicate that these areas were formed by lava flows from Terevaka at some point, indicating that there is clearly some level of threat.  Yet these areas are far enough away from possible vents that the likelihood of being hit by a flow is decreased, and the time available for one to escape in the event of an eruption considerable.

Hanga Roa Post Office16

       Hanga Roa, the island’s only town/village and therefore essentially the location of the entire population, is partially located within the area threatened by lava flows (though not pyroclastics/tephra).  It is visible on the SW corner of the island.  The decision must therefore be made whether it is worth investing in a system or evacuation plan to protect this area from potential activity.  Because an eruption is so unlikely, and because any activity that may occur has only a small chance of originating in the areas that may threaten Hanga Roa, it simply is not necessary to undergo large scale preparations.  Something like a Public Address system in town might be a worthwhile investment as it can be utilized in other ways during the extended periods of inactivity, but mock evacuations and large-scale volcanic preparation projects would likely be nothing more than fear-mongering.  Easter's isolation would also make such drills cost-prohibitive, and the damage to a largely tourist economy would undoubtedly be great.

Why no evacuation plan?