You have probably seen this film, taken by Gary Rosenquist on May 18, 1980:
https://youtu.be/EMVCLpuTKwM&end=18
Try to imagine the landslide happening in deep water, say, at one of those southern Pacific Island volcanoes.
What would that look like?
It did happen, but in 1888, so there’s no video of the event. Today, the remains of the largest island collapse in recorded history look like this:
https://youtu.be/Ihh6_j-jBII&rel=0
Like Graniya at Volcano Hotspot, I first heard about Ritter Island through R. Wally Johnson’s Fire Mountains of the Islands.
According to Johnson, German colonials on a relatively distant island in the area noted:
…a noise like thunder was heard shortly after 6.30 in the morning, and at the same time the sea and the water in the harbour started to move with surging rapidity in such a way that it flowed up and down and the ships in the harbour were in danger. The water fell so sharply that the reef south of the wooded island Madang was dry in 2 minutes and stood 5–6 feet out of the water. Then the water came back with the same force. The time between the lowest and highest level was 3 to 4 minutes, the speed of the current was reckoned to be 8 to 10 knots … After the arrival of the tidal wave [tsunami], some observers noticed a fine, barely perceptible rain of ash.
Everyone soon discovered that Ritter, out in the strait, was mostly destroyed. Johnson notes that at first people thought that the known volcanic island had exploded like Krakatau had done five years earlier — only there was little evidence of an explosive eruption.
According to him, the mystery of Ritter Island wasn’t solved until the May 1980 sector collapse at Mount St. Helens showed geoscientists what to look for.
It’s likely that Ritter did a St. Helens but without the accompanying major eruption. Nevertheless, this debris avalanche caused a big tsunami.
Here is one possible scenario by Dr. Steven Ward (I don’t know if a consensus exists yet on the event):
https://youtu.be/-KaMttI3fk0&rel=0
That other volcano, at the end, is Ulawun.
In that era, the death toll of natives was not documented very well. Brown et al. put it at 1,650; in the video earlier in this post, the GEOMAR people almost double that figure. We likely will never know for sure how many perished.
All we can do today is try to understand the hazard better and take whatever steps are possible to reduce the risk before another volcano-induced tsunami occurs — here or elsewhere in the world.
Lagniappe:
https://youtu.be/BFNekjEgvuk&rel=0
Featured image: Christian Berndt/Eos
Sources:
Brown, S.K.; Jenkins, S.F.; Sparks, R.S.J.; Odbert, H.; and Auker, M. R. 2017. Volcanic fatalities database: analysis of volcanic threat with distance and victim classification. Journal of Applied Volcanology, 6: 15.
Johnson, R. (2013). Fire Mountains of the Islands: A history of volcanic eruptions and disaster management in Papua New Guinea and the Solomon Islands. ANU Press. https://openresearchlibrary.org/content/84395a8e-81fb-452f-a7bb-41ec37ce62f7
Zorn, E. U.; Orynbaikyzy, A.; Plank, S.; Babeyko, A.; and others. 2022. Identification and ranking of volcanic tsunami hazard sources in Southeast Asia, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2022-130, 2022.
Flight To Wonder 