From the “How not to console” department…
In order to assure folks that the area of the Leilani Eruption of Kilauea is NOT going to slide off into the sea, the USGS explains that it is only “slumping” slowly into the ocean in a more normal way and that won’t cause a tsunami at all.
Bold bits bolded by me.
Facts on the stability of Kilauea’s south flank, past and present.
May 14, 2018
There have been several recent highly speculative stories, rumors and blogs about the stability of the south flank of Kilauea and the potential for a catastrophic collapse that could generate a Pacific-wide tsunami. We wish to put these speculations in their proper context by presenting observations of the current situation and an assessment of past evidence of landslides from Kilauea.
There is no geologic evidence for past catastrophic collapses of Kilauea Volcano that would lead to a major Pacific tsunami, and such an event is extremely unlikely in the future based on monitoring of surface deformation. Kilauea tends to “slump”, which is a slower type of movement that is not associated with tsunamis, although localized tsunamis only affecting the island have been generated by strong earthquakes in the past.
Oh, so it won’t land slide it will only land slump; I’m so much relieved. No tsunami for California then.
The May 4 M6.9 earthquake resulted in seaward motion of approximately 0.5 m (1.5 ft) along portions of Kilauea’s south flank as measured by GPS stations across the volcano. A preliminary model suggests that the motion was caused by up to 2.5 meters (8 feet) of slip along the fault that underlies the volcano’s south flank, at the interface between the volcano and the ocean floor, about 7-9 km (4-6 mi) beneath the surface. This motion is within the expected range for a large earthquake on this fault. The earthquake was probably caused by pressure exerted by the magmatic intrusion on the south flank fault, following the pattern of past earthquake activity that has been observed during Kilauea East Rift Zone intrusions. A small, very localized tsunami did occur as a result of the fault slip. Similar local tsunamis were generated by past large earthquakes, including the 1975 M7.7 and 1868 ~M8 events, both of which resulted in multiple deaths along the south coast of the Island of Hawaii.
Hey, it’s only moved 1.5 feet at the surface ( 2.5 meters or 8 feet down at the actual fault ). It’s only a 5 mile +/- thick slab doing the “slump” anyway… And it is “expected”. We all know that if you “expect” at tornadoes and hurricanes they don’t hurt you either, so why would a volcano be any different? We ALL need to get our attitude straight and start “expecting” at the volcano so it acts nice. (While we are at it, remember that this power of “expecting” is likely why the Global Warmistas hate the Deniers – it is all our fault for not properly “expecting” Global Warming, as clearly failure to “expect” enough lets The Bad Thing happen… /sarc;)
I also like the way they point out that the lava flowing into the dikes is acting as a hydraulic ram sliding that slab over “caused by pressure exerted by the magmatic intrusion”. So I guess we just hope that the pressure stays constant? No, that’s making it move… We hope that the pressure decreases? I really need to know what I’m supposed to “expect” so I can do my proper job of expecting to keep The Bad Thing away.
Adjustments on the south flank caused another ~9 cm (3.5 inches) of motion at the surface in the day after the earthquake, followed by another 2-3 cm (~1 inch) since May 5. This is higher than the normal rate of south flank motion (~8 cm (3 inches) per year) but is expected as the volcano adjusts after a combination of a magmatic intrusion along the East Rift Zone and a large south flank earthquake. We did observe minor ground ruptures on the south flank, but this is expected given the strength of the May 4 earthquake, and deformation data show that the south flank continues to move as an intact slump block.
Geologic history combined with models of south flank motion suggest that the likelihood of a catastrophic failure event is incredibly remote. There are certainly signs on the ocean floor for landslides from other volcanoes on the Island of Hawaii and from other islands, but none are associated with Kilauea. In addition, Kilauea has experienced much larger earthquakes and magmatic intrusions in the recent past. The large earthquakes of 1975 and 1868 were not associated with significant south flank landsliding, nor were major East Rift Zone intrusions in 1840 and 1924.
So it’s normally “slumping” some every year, and it did speed up with the quakes and the lava and all, but it, too, is “expected”. Oh, and I’m Sooooo happy to know that “the south flank continues to move as an intact slump block” and is not breaking up as it “slumps” toward the sea. And as long as we don’t have too many earthquakes, it will be slow enough nobody will notice. Well, other than the fissures and the lava and all… but that’s “expected”…
Besides, all the OTHER SLUMP failures into the ocean and the landslides of massive chunks causing huge tsunami events have only happened “from other islands” and “none are associated with Kilauea”. So just ’cause the other islands and volcanoes do it doesn’t mean this one will do it… well, at least not now. It’s just not expected now. (One hopes this lack of expecting does not let this Bad Thing sneak past the expectation barriers protecting the Big Island…)
So no worries, eh? This is just the volcanoes way of getting a little wiggle room for it’s fissure toes. Just gently shoving a few miles thick section of flank over a little bit, just a few meters, making room for some more island below the surface. I mean, it’s a feature, don’t you see? Otherwise all that lava would have to flow over the surface to get more room for more island. We’ve seen how that works out. ( I guess not enough folks were expecting it… Bad Tourists!)
The hilina slump a.k.a. “the big crack”
Huge chunks of the Hawaiian Islands have been sliding into the Pacific Ocean for hundreds of thousands of years. (SF#101) Geologists classify these slides as either “slumps” or “debris avalanches.” Slumps move just a few inches a year but are prone to bigger, jerky adjustments. Debris avalanches are fast cascades of rocks and soil. In Hawaii, both varieties of movement can involve massive blocks of real estate. In the huge Nu’uanu debris slide, stone blocks 6 miles across tumbled 30 miles out to sea. Both slumps and debris slides may create colossal tsunamis. (Tsunamis are miscalled “tidal waves,” but they have nothing to do with tides and do not behave like tides or wind-driven waves.)
When large pieces of the Hawaiian Islands slip into the ocean, the entire Pacific Rim is smashed by the resulting tsunamis. In New South Wales, Australia, there is geological evidence that part of this coast was scoured by a Hawaii generated tsunami 100,000 years ago. The postulated wave started out about 375-meters (½-mile) high in Hawaii. By the time is reached Australia, it was about 40 meters high. (SF#85)
Worse waves may be on tap. A 4,760 cubic mile chunk of the Big Island (Hawaii) is breaking away at the rate of 4 inches per year. This is the Hilina Slump, and it is said to be “the most rapidly moving tract of ground on Earth for its size.” The Hilina Slump can move much faster. At 4:48 AM, November 29, 1975, a 37-mile-wide section suddenly dropped 11½ feet and slid seaward 26 feet. The result was a magnitude-7.2 quake and a 48-foot-high tsunami. This was a minor of the slump. If the entire 4,760-cubic-mile block decided to break off, it would probably create a magnitude-9 quake and a tsunami 1,000-feet high. All the coast-hugging cities of the Hawaiian Islands would be swept away. And LOOK OUT Australia, Japan, and California.
(Napier, A. Kam; “Landslide,” Honolulu, p. 28, February 1997. Cr. H. DeKalb.)
But no reason to expect that. It isn’t likely. Not right now. It will only be likely after is has a sudden “jerky adjustment”.
The Nu’uanu debris avalanche contains enormous blocks ~30 km long, 17 km wide, and at least 2 km tall. The landslide is spread over a 23,000 km2 area.
The Tuscaloosa seamount or debris from the Nu’uanu debris slide is one mile deep and over 135 m2 in area. This rivals the size of the city of Atlanta.
Nu’uanu debris extending 150 miles from the island is the size of the state of New Hampshire.
Scientists have identified over fifteen giant landslides surrounding the Hawaiian Islands.
Frequent landslides from Koolau Volcano: Results
from ODP Hole 1223A
Michael O. Garcia, Sarah B. Sherman, Gregory F. Moore, Robert Goll, Irina Popova-Goll, James H. Natland, Gary Acton
Accepted 15 July 2005
Available online 16 November 2005
Giant landslides on the flanks of oceanic islands are considered relatively rare but potentially devastating natural hazards. The Hawaiian Islands are known to produce some of the biggest landslides on Earth. The Nuuanu slide, largest of the Hawaiian slides, is thought to have removed a substantial part of Koolau Volcano from the island of Oahu. Ocean Drilling Program (ODP) Hole 1223A was drilled to determine the depositional history, timing, thickness and hazards associated with the Nuuanu landslide, the only previously known Koolau slide. Site 1223, located ~260 km northeast of the island of Oahu near the crest of the 500-m-high Hawaiian Arch, was drilled to a depth of 41 m. Eight distinct sandy layers were recovered and more are likely to occur deeper in the section. Contacts of these sandy layers with pelagic clay are sharp at their base and gradational at the top. The layers contain angular fresh glass fragments with compositions that are typical of Hawaiian shield volcanoes, including the distinctive Koolau high SiO2-type in seven layers. Most glasses ( > 90%) are degassed ( < 0.03 wt.% S) indicating that they were probably erupted subaerially. Pleistocene to Early Eocene Radiolaria taxa are present in the Hole 1223A cores, with mixed ages in some intervals. Seven of the sand layers are probably associated with Koolau landslides and were deposited prior to 1.77 Ma. Among the four thicker sand layers ( > 1.5 m), it is unclear which, if any, are related to the Nuuanu slide. Results from Hole 1223A cores demonstrate that Hawaiian volcanoes collapse repeatedly, and the debris from these many slides can travel great distances ( > 260 km) across the ocean floor and over significant bathymetric obstacles (~500 m). Thus, landslides from oceanic volcanoes pose a greater risk than previously assumed.
But just because they are a regular feature of the Hawaiian Islands and “pose a greater risk than previously assumed” and happen repeatedly as the islands age and the basaltic rock weathers; that’s no reason to expect them. After all, these things happen on geologic time scales. The odds are quite small in any one decade, or even century. Nearly zero in fact. Until it happens.