The recent earthquakes are unusual for this region. Previously any tremors were from “volcanic” activity. This time it is quite different, as reported below by GeoNet:
Some minor earthquake activity is being observed at Mt Ruapehu.
GeoNet reports that in addition to a recent drop in lake temperature, in recent weeks Ruapehu has experienced some minor earthquake activity.
“Although the nature of the earthquakes is quite uncommon for Ruapehu, our analyses since our last bulletin do not raise any concerns,” says a GeoNet spokesperson.
“Other monitored parameters have not changed since last week’s bulletin, and volcanic activity remains low. The Volcanic Alert Level remains at 1 and the Aviation Colour Code at Green.
“In early March 2024, we first observed an uncommon style of small earthquakes at Ruapehu. Subsequent re-examination of seismic data has revealed those earthquakes commenced at least as early as mid-February.”
GeoNet says the earthquakes are small and were initially difficult to identify without careful examination of the data as they are uncommon at Ruapehu and only the larger examples are detected by our automatic systems.
Over the last month, GeoNet has seen a maximum of six of these earthquakes a day, and on many days none at all.
Each earthquake consists of up to about 10 minutes of ground shaking, and is composed of a number of similar sub-events.
“While we are able to determine a location for some of the larger examples, the small size and style of the activity means our locations, especially depth, are quite uncertain.
“However, as they are recorded only by monitoring stations on the upper part of the volcano, we speculate that they originate near the summit area of the volcano within a few kilometres’ depth beneath the surface.”
As the earthquakes do not typically last more than 10 minutes, they do not constitute volcanic tremor, and that remains low.
The earthquakes are also quite different in appearance from volcanic tremor traditionally seen at Ruapehu.
“While the earthquakes represent something new at Ruapehu, and we are working on understanding the details of the processes driving them, they are not thought to pose any concerns for eruptive activity,” says GeoNet.
“Other monitored parameters have shown no recent changes. The temperature of Te Wai ā-moe (Crater Lake) is now relatively stable at about 24 ºC, recent observations of the lake recognised nothing unusual, gas emissions from Ruapehu remain moderate, and volcanic tremor is low.
“Monitoring indicators remain consistent with a low level of volcanic activity. As a result, the Volcanic Alert Level remains at 1. The Aviation Colour Code remains Green.
“Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of minor volcanic unrest.”
The Volcanic Alert Level reflects the current level of volcanic unrest.
The Volcanic Alert Level should not be used to forecast future activity.
Volcanic Alert Level 1 indicates the primary hazards are those expected during volcanic unrest: steam discharge, volcanic gas, earthquakes, landslides, and hydrothermal activity.
While Volcanic Alert Level 1 is mostly associated with environmental hazards, potential for eruption hazards also exists and eruptions can still occur with little or no warning.
Volcanic Alert Levels 3, 4 and 5 are reserved for eruptions with varying impact distances.
For information on access to the Mt Ruapehu area, please visit the Department of Conservation’s website on volcanic risk in Tongariro National Park and follow the DOC Tongariro Facebook page for further updates.
For information about responding to volcanic activity there are guidelines from the National Emergency Management Agency.
GNS Science and its National Geohazards Monitoring Centre continue to closely monitor Mt Ruapehu for further changes.
(Six years ago the Bridge Pool was still the most popular and productive trout fishing pool in NZ.)
Do earthquakes affect the trout fishing in Turangi?
Below is the Bridge Pool TLB combat casting team during spawning runs – the most popular trout fishing pool in NZ.
Last week in particular the Tongariro trout fishing was described as either “hot” or “cold”.
Several regular TRM fishos could not understand it when they went home empty-handed after such a long period of good catches by others. This is serious stuff as the Tongariro has a world-famous reputation to maintain. So TRM needed to come up with a simple believable explanation…
The Tongariro River often have days or periods when suddenly the hook-up pattern changes from everyone easily catching fish, to suddenly no trout? This is not unusual. For no apparent reason suddenly for a few hours or a day or two all the trout seem to go off the bite. Why?
We know they are resting there. In some pools we can see them, but they refuse to even look at anything offered. They just freeze up. Spooked. Why?
This is SWMBO’s explanation. (She Who Must Be Obeyed is the manager who knows everything at TRM) She has no doubt about the reason. But, if I may be so blunt, She may often be completely wrong, but never in doubt. Of course other Tongariro anglers will have their own theories. All are correct. We have to believe them all. Our guests are always right. But you need to be warned this is all wild guess-work as, we remind you again, that nobody, not even SWMBO, has interviewed the trout yet. But Her reason may be as plausible as any…
This volcanic region is subject to earthquake swarms that we cannot physically feel or detect but the trout are far more sensitive to tiny earth tremors. The deep pumice sub-strata absorbs much of the shocks for humans to feel but these tremors are exaggerated in water. Trout are far more sensitive. The sense organs and lateral line on the trout picks up any earth tremors far more effectively so they spook and stop feeding.
Tiny earthquakes in this shaky region are a regular normal phenomena and not considered of much importance until they affect the fishing. Then they have to be seriously considered.
So this is SWMBO’s proof to justify Her explanation:
Many wonder why the bridge pool is so successful. On Friday and Saturday mornings there were about 9-10 anglers there each morning and trout continued to be caught most of the day just below the bridge. (This is the closest most popular pool to TRM – just a couple of hundred metres waddling in waders…)
SWMBO applies the same loopy earthquake theory. The trout on their spawning runs “hear” the vibrations from traffic crossing the bridge and will not continue under the bridge. Slowly their numbers build up all day. At night there is little traffic volume so the trout then swim under and continue their journey. Seems a reasonable understandable explanation… OK?
About the Lateral Line
Trout have inner ears, which allow them to hear sounds as we do. They also have lateral lines, special sense organs used to “feel” sounds. Lateral lines allow trout to hear sounds that are too low for humans to hear. Every trout has two lateral lines, one on each side of its body. A lateral line is made of a series of U-shaped tubes. Every time the water outside the U vibrates because of a sound, a tiny hair at the base of the U wiggles, which sends a nerve signal to the brain. The trout’s brain translates the wiggle into information about where the vibration came from. Trout use lateral lines to find food, escape predators and keep away from obstacles.
Sometimes I suspect SWMBO has a lateral line too.
Wikipedia explains:
Lateral line
From Wikipedia:
The lateral line is a system of sense organs found in aquatic vertebrates, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial cells, known as hair cells, which respond to displacement caused by motion and transduce these signals into electrical impulses via excitatory synapses. Lateral lines serve an important role in schooling behaviour, predation, and orientation. For example, fish can use their lateral line system to follow the vortices produced by fleeing prey. Lateral lines are usually visible as faint lines of pores running lengthwise down each side, from the vicinity of the gill covers to the base of the tail. In some species, the receptive organs of the lateral line have been modified to function as electroreceptors, which are organs used to detect electrical impulses, and as such, these systems remain closely linked. Most amphibian larvae and some fully aquatic adult amphibians possess mechanosensitive systems comparable to the lateral line.[1]
Function
The lateral line system allows the detection of movement, vibration, and pressure gradients in the water surrounding an animal, providing spatial awareness and the ability to navigate in the environment.
So now you know…
