The expression became famous because of Isaac Newton. Never one to ignore praise, in typical English fashion he expressed his self-assured superiority in a self-effacing way: “If I have seen further it is by standing on the shoulders of Giants“. This was written in a letter to Robert Hooke, himself both an intellectual giant and a person with power who could be morose, jealous and vengeful. Newton’s confession should perhaps be seen as a way to keep favour with someone who could (and would) become a powerful enemy. And of course, it doesn’t really reduce the dwarf. The point is that the dwarf does see further than anyone else. Rather than putting oneself down, it puts the writer on a pedestal.
But the expression was not original: Newton quoted older sources. The oldest written source containing it is from 1159, the Metalogicon (meaning ‘on behalf of logic’) by John of Salisbury (names were so easy in those days), where he writes “Bernard of Chartres (another easy name. Imagine being called ‘Bob from New York’) used to compare us to dwarfs perched on the shoulders of giants. He pointed out that we see more and farther than our predecessors, not because we have keener vision or greater height, but because we are lifted up and borne aloft on their gigantic stature.”
But make sure you stand on the shoulder of the giant, and not on its knee. Otherwise you still remain the lower of the two. This mistake is a very common one in real life. To benefit from prior knowledge, you need to learn all of it, not ‘just enough’ to get by.
Kilauea also made this mistake. In comparison to other prime Hawai’ian volcanoes, it is not large. It got a head start by growing on top of the lava of Mauna Loa, the giant next door. But it started out too low down the Mauna Loa slope to become the dominant seer.
In this blog, Mauna Loa is often portrayed as being in decline and no longer important. Here I will argue that far from this, it is still the mover and shaker of Hawai’i. Even of the dwarf on its knee, noisy Kilauea.
Mauna Loa is the world’s second tallest volcano on Earth, after Mauna Kea. It started 5 km below the sea, and took around a million years to reach its current height of 4.17 km above sea level. Although it is slightly lower, Mauna Loa is a lot bigger than Mauna Kea. Mauna Loa is a shield volcano: its fast flowing lava has spread far, building a large mountain with a shallow slope. It is much wider at its base than Mauna Kea, has much more volume and therefore much more mass. This is immediately obvious from satellite images
Mauna Loa is a very elongated mountain. It is a lot longer in the southwest-northeast direction. In fact, the name Mauna Loa means ‘long mountain’. The long ridge follows the rift zone. There is a caldera at the top (which shows the mountain used to be a little higher before the collapse); the rift extents from the caldera towards the south west and towards the east, running from the south eastern point of Hawaii to (almost) Hilo, a distance of almost 100 km. The southwest rift bends by 40 degrees some 30 km from the summit, at an altitude of 2400 m. At the location of this bend a number of eruptions have build a satellite shield. The northeast rift also bends, to the east, but this bend happens much closer to the summit.
On the satellite image (which predates Leilani), the extent of the lava flows give a good indication of which volcano rules which area. The edge of Kilauea’s dominion is clearly visible. The lava flows from Mauna Loa reach very close to the summit of Kilauea. Kilauea owns the land to the south and east from its summit, but very little to the northwest.
Let’s look at those dominions. On the map, the two circles show the area of dominance of Mauna Loa. Of course it is not exactly a circle, but it gives an idea. The inner circle extends to the lava field of the neighbouring volcanoes, a distance of 27 km. The outer circle is the distance to Kilauea’s conduit. (The distance from Mauna Loa to Kilauea is 34 km, according to giggle maps – which also claims you can walk it in 14 hours, something I have doubts about.) Distances between neighbouring volcanoes on the island of Hawai’i are quite similar:
Mauna Loa to Mauna Kea: 41 km
Mauna Loa to Hualalai: 37 km
Hulalai to Mauna Kea: 44 km
Mauna Kea to Kohala: 40 km
Hualalai to Kohala: 46 km
Mauna Loa to Kilauea: 34 km
The separation is about the same as the depth of deepest magma, which is not accidental. A new volcano can only form at a certain distance from an existing one. Magma will always prefer to use an existing conduit within reach, rather than spending effort in forming a new one. But if the distance to the conduit becomes larger than the depth, then it becomes easier to form a new conduit. Both Mauna Loa and Kilauea are fed by 30 to 40-km deep conduits. (There are of course many intermediate magma reservoirs on the way, where the magma can age before use.) Pahala’s earthquake activity also has this depth of 30 to 40 km and it is at this same distance from both Mauna Loa and Kilauea. This may be the reason why the magma is congregating underneath Pahala, unsure what to do next.
Kilauea is a little closer to the Mauna Loa than would have been predicted from the other volcanoes. This might be why it hasn’t grown as large yet: there is competition for its magma supply.
All Hawai’ian volcanoes have rift zones: it is part of their culture. These rift zones are indicated by the dashed lines on the map below. (The rift zones extend further than shown on the map, and can reach as fas as the deep ocean.) Those rifts deserve a closer look.
A curious aspect is that the rift zones tend to run parallel to the nearest neighbour volcano.
Consider Kohala, the oldest volcano on the island. It’s rift zone runs parallel to Hualalai, the next oldest, but not to Mauna Kea which is a bit younger. Mauna Kea has strongly bend rift zones: it was clearly affected by its older neighbours. On the eastern side the Mauna Kea rift seems to bend and merge with the rift of Kohala. Off-shore it becomes the Hilo ridge which seems to have been owned both by Kohala and Mauna Kea. Hulalai’s rift runs parallel to Kohala and Mauna Kea, but is unaffected by Mauna Loa which did not yet exist in Hualalai’s glory days.
The southwestern rift zone of Mauna Loa runs parallel to Hualalai, and the northeastern one parallel to Mauna Kea. In the far southwest, the 40 degree bends brings the rift into line with that of Hualalai, similar to the case of Mauna Kea at the other side of the island. The bend in the northeast rift is due to Mauna Kea. Clearly, the rift zones show the interaction where younger volcanoes had the follow the guidance of the older ones. They are perpendicular to the flank of the older, larger (at the time) volcano, and in fact follow the same direction as the pali of the older volcano would. A rift perhaps begins as a slump in the other volcano. Once the rift is established, it will remain in place while its owner grows, although it can (and does) grow in extent, away from the mountain.
Kilauea’s rift zone runs parallel to Mauna Loa and follows the elongated shape of Mauna Loa. It is clearly very strongly affected by Mauna Loa.
An interesting effect is that Kilauea’s rift zone of offset from its summit by about 7 km, while for Mauna Loa the rift zone goes exactly through the summit. All other Hawai’ian volcanoes also show perfect alignment of the rift zone with the summit. Kilauea is the odd one out.
The rift zones are the locations of most of the earthquakes. Rifts are a weak zone where magma can force its way in; the earthquakes can happen during these intrusions or during tectonic adjustments. Magma intrusions typically happen as a dike, 1-3 km in height, 10 km or more in length, but as little as 1 meter in width. The magma forces the rift apart. A dike can slowly melt its roof. Sometimes, when a dike runs close to the surface, on one or more places along the dike the roof can collapse: this forms one or more pit craters. Kilauea’s pre-2018 lava lake first formed in such a collapse crater where the magma below melted an opening, providing a window into the flow. That magma had no intention to erupt there: it was on the way to Pu’u’O’O’o, and the pit lava lake was just a distraction on the road. Summit calderas can become enlarged by such pit craters: eventually they can become elongated as a result. Halemaumau itself started as such an off-centre pit crater, perhaps around 1825.
In addition to the rift zones, there are fault zones. These are distinct from the rifts. As mountains grow and summit rifts expand, the slopes of the volcano are pushed outward. This movement occurs on faults. It will not be a surprise that these faults tend to run parallel to the rift zones. In the case of Kilauea, the main faults run south of the rift zone but not on the north. This is because the massive bulk of Mauna Loa blocks any expansion to the north.
There are two obvious fault zones south of Kilauea. One is the Hilina fault, which follows the steep escarpment at the edge of the island. The second is the Koa’e fault which is visible on the surface south of the caldera, and which joins the east and west rift zones. The Koa’e fault can erupt lava, but the dominant signature is ground cracks, grabens and low cliffs (scarps). Just south of the Koa’e fault, the land is moving towards the sea at 8 cm per year. There are frequent earthquakes here, which in 1965 uplifted part of the area by more than 2 meters. The whole region may be unstable, and in a distant future it is conceivable that the entire block south of the Koa’e fault zone will slump into the ocean.
The Hilina fault also is very visible on the surface, with a cliff several hundred meters tall. It traces a large slump, where material moved towards the ocean and left the cliff behind. Perhaps one day the Koa’e fault will look like this. But the real Hilina fault lies several km underground. How deep it goes is not really known. The lava pile here is 9 km deep, and underneath this is the old ocean floor. The contact plane (decollement) between the lava and ocean floor is nearly horizontal: it is tilted by 5 degrees. (The downward direction is north, where the ocean floor is depressed by the weight of the mountains.)
The best description is obtained of course from USGS. This drawing is from them, with as only VC addition a rough indication of the Hilina fault. (VC is a dwarf standing on the shoulders of USGS!)
As indicated in the drawing, the dike pushed out the land in the upper few kilometers. But the contact plane with the ocean floor (‘Pacific plate’ in the picture) is locked in place. The top moves, but the bottom doesn’t. (After 10 months of lock-down, I feel the same way!) This difference in movement causes shear between the top and the bottom. The pull on the bottom grows every year, until finally it gives. Now the bottom moves seaward (5 degrees uphill!) by potentially several meters. At the point where it begins, the top will sink, forming the cliff (or pali). This is the cause of many of the largest earthquakes in the area, including M7+ events such as in 2018. Here the stress comes from the expanding rift, but the inflating caldera can do the same thing. And even without inflation, just the height of the summit puts an outward force on the slopes and try to make it move.
In practice, the surface is connected to the deeper regions by a number of steep faults, which accommodate the shear. One of these is the Hilina fault. It appears that the Hilina fault does not connect all the way to the bottom but remains fairly shallow. Some earthquakes cause it to move, with potential tsunami consequences, but not all do. The 2018 event did not.
When push comes to shove
Now let’s look again at Mauna Loa versus Kilauea. What does a giant do when a dwarf climbs on its shoulder?
Mauna Loa is of course a far older volcano. It started out a million years ago, first on the sea bed and afterwards on the land it itself created. The growth has not been uninterrupted. On the west side, about 100,000 years ago a large block broke off and collapsed into the sea, with debris flowing out as far as 80 km. The scar and its debris are still visible. And while the Hilina slump happened slowly (mostly), this one happened in one collapse.
The south east side of Mauna Loa has suffered large, slow slumps similar to Hilina, leaving scars or palis. Some still exist (the Ninole hills above Pahala), others have been buried under new lava flows. The slumps left us with old faults, now largely inactive. One of these is the Kaoiki fault zone, which follows the buried palis between Kilauea and the Mauna Loa summit. The Kaoiki zone is still active; in recent years it has caused damaging earthquakes in excess of M6. The Kaoki zone extends close to Kilauea.
Kilauea began to grow just below the old pali. Was this accidental? It is difficult to know. A major removal of material can allow magma an easier pathway to the surface. Once that pathway existed, the location was far enough from Mauna Loa (just) to retain its own magma supply and declare independence.
The oldest Kilauea lavas are up to 300,000 years old. They were in part submarine: the pali may have been at the coast. At first eruptions happened at different places along the flank of Mauna Loa in shallow water, with some above sea level. Some of the lava formed sand, as it does when flowing into the sea. Kilauea may have formed an island. But there was also eruption at deeper levels on the southern flank, far from the rift zone. It is not known whether there was already a central vent and burgeoning rift zone, or that (like the current activity of Mauna Kea) the eruptions came from scattered locations. This pre-shield phase lasted until 130,000 years ago.
While Kilauea grew – slowly -, Mauna Loa was still spreading. The massive weight of its edifice and the magma insertion in the rift zone pushes the sides out. One of the remarkable things about Mauna Loa is that it maintains it height in spite of this spreading. A lot of its magma is not used for eruptions, but fills in the gaps, keeping up appearances and increasing the bulk. Volcanoes should not just be judged by the surface activity but also by their internal magma digestion. Kilauea, build on the slope of Mauna Loa, was carried outwards by the spreading of Mauna Loa. But once the conduit was established, that conduit would not move. So the eruptive summit stayed in place, while everything else was moving south, away from Mauna Loa. This is perhaps how the rift zone ended up 7 kilometers (estimated) from Kilauea, and why no other Hawai’ian volcano shows such an offset. It is the effect of standing on a giant. When the giant moves, so do you. You have to go with the flow.
From 130,000 years ago, the Puna ridge quickly grew, and Kilauea entered the shield-building phase. The timeline shows that Mauna Loa was already half a million year or more old before Kilauea started. Mauna Loa must already have been a very large volcano, and Kilauea always was a small bump on a much larger giant. Over time, Kilauea was pushed up both by its own growth and by the further expansion of Mauna Loa. But even now, Kilauea isn’t particularly high (1247 m, to be precise). To put Kilauea’s origin near sea level on an already large Mauna Loa means that its own growth has been modest. It indicates that Kilauea is relatively thin, and that its lava pile is little more than 3 km thick. Below that lies the pre-existing Mauna Loa lava.
This makes Kilauea a still very young volcano. It is a teenager, not so much a dwarf as a child carried by its giant parent. The lava flows are no more than 3 km thick, underlain by 6 km of Mauna Loa flows. The volume of Kilauea becomes between 5000 and 10,000 km3. Over 100,000 years of growth, the average lava production is 0.05 km3/yr. The current rate is twice as large; allowing for a slower start these numbers appear reasonable. And it explains why, in spite of all its activity, Kilauea remains little more than a bump on the landscape, dwarfed by Mauna Loa. Its adolescent growth spurt is still to come
On the figure above, the Hilina fault is (speculatively) shown as extending down 3 km, from the pali to the contact between the Kilauea and Mauna Loa lavas. The contact between the Mauna Loa lava and ocean floor is much deeper.
Kilauea has changed Mauna Loa. It acts as a buttress, and has fixed the southeast slope of the mountain. It is no longer able to shift downslope in the way it used to do. Slumping is stopped by the new bulk of Kilauea. But movement along the bottom still remains possible.
Of the ancient faults on the southeast flank of Mauna Loa, one remains active: Kaoiki northeast of Kilauea. The fault system predates Kilauea. There are steep faults which follow the old pali; deeper down is a near horizontal fault, the decollement between the lava pile and the ocean floor.
There are two different types of earthquakes here. The larger ones (1962, 1983, both M6+) occur higher up the slope of Mauna Loa, have a depth of 8-11 km and are nearly vertical strike-slip. They cause surface ruptures. The second type consists of swarms, with individual events up to M4. They occur close to the Kilauea summit. This activity here does not reach the surface – the movement stays well below ground. A 9000-year old lava flow has been left unbroken.
One of these swarms started on Oct 22, 2020, located a few kilometers west of Kilauea’s summit, near Namakanipaio Campground. This is just below the ancient Mauna Loa pali. The largest single event was a M3.5 earthquake. The quakes were shallow, 2-5 km. It was the 6th such swarm since 1983. The most recent one before 2020 was in 2012.
The swarm had no effect on Kilauea, in spite of being in its vicinity. That is also true for the earlier swarms. But the summit of Mauna Loa, much more distant, showed a pronounced effect. Over a few days it deflated by a centimeter (a lot, for a mountain this size), and the caldera contracted by a similar amount. The change started at the same time as the swarm. It is not clear which one was the cause and which one the effect! The Mauna Loa summit remained deflated until late December when it quickly reversed. As of this week, Mauna Loa is back to its pre-swarm size, and is rapidly expanding.
What happened? USGS has not left us with clear guidance on this, so we have to guess (speculation alert), based on what we do know. The change in Mauna Loa was unusually strong and fast. There has been no other comparable event over the past 5 years – not even during Leilani.
My guess is that this was a downward shift of Mauna Loa in the direction of Kilauea. There was no notable effect on Kilauea, nor was there any ground movement. Neither did the GPS measurements catch horizontal shifts. Therefore, the movement happened underground, below the bulk of Kilauea. The swarm was nowhere deep enough to happen on the boundary between the Mauna Loa lava and the old ocean floor, but it does fit the upper boundary. The lava pile of Kilauea is 3 km thick, and this is also the approximate depth of the swarm. This potentially puts the earthquakes at the decollement between Kilauea and the underlying Mauna Loa lava. The Mauna Loa lava was on the move, but it left Kilauea in place. The underground downward movement reduced the pressure on the shallow Mauna Loa magma chamber; over a few days the magma chamber adjusted and this caused the deflation at the summit.
It has been suggested that Kilauea grew on top of a layer of sediment. Such a soft layer could help accommodate the slide, and could cause the movement to occur in swarms of small events, rather than a big quake. The deeper decollement with the ocean floor shows large quakes (such as the 1868 M7.9 Ka’u quake), aseismic creep, and regular slow-slip events. Underneath the Kilauea summit, it makes sense that the upper contact plane also shows movement, leaving the summit itself in place.
The unexpected eruption
We can take this model one step further (speculation alert). Forty days after the swarm happened, a dike nearly broke the surface at Kilauea. Twenty days later, a second dike did break through and started the Kilauea summit eruption, still on-going and forming a rootless lava lake already more than 210 meters thick. (As I write this, it is the first day the new lava lake has gone down rather than up (by 1 meter), and perhaps the eruption is nearing its end.) Perhaps the eruption was not a coincidence. It did not follow instantly after the swarm and Mauna Loa’s deflation, but the process may have been started by it.
The Kilauea summit has a number of magma chambers, at various depths. A very shallow chamber is suggested to be at a depth of some 2 km, and this is feeding the current eruption. A second chamber is suggested at 3-4 km depth and a third chamber at 8-11 km. Earthquakes tend to happen at these depths. It is a very complex region and very difficult to map. The deeper chamber seems to lie at the depth of the decollement between the lava and the old ocean floor, extending into oceanic crust. The intermediate chamber may lie at the contact plane between the Mauna Loa and Kilauea lavas. Magma finds it easier to form sills at such planes, which form a structural weakness.
A shift of the top of the Mauna Loa pile may have increased pressure on the intermediate magma chamber which lies in this region. The pressure caused magma to begin moving upward, and after a month enough pressure had transferred to begin breaking open the route to the surface. And so the eruption began, and this new pressure is why it is lasting unexpectedly long.
The idea behind this model is that the Mauna Loa pile is moving, but that the summit region of Kilauea remains in place, fixed by its magma chambers. The rift zone is not so lucky. It follows a structural weakness in the rock, and as the pile moves down, it takes the rift zone with it. The southern slope moves as much as 8 cm per year. Over 100,000 years, that amounts to 8 km, and this is indeed about how far Kilauea’s rift has moved away from the summit.
This is speculation. Is it right? It is a model that fits the data we have. There may be data we do not have and cannot see. But isn’t it nice to think that Mauna Loa could squeeze an eruption out of its little neighbour?
Albert, February 2021
(The title of the post is plagiarised from the paper: ‘Piggyback tectonics: Long-term growth of Kilauea on the south flank of Mauna Loa’, Journal of Volcanology and Geothermal Research, by Peter W. Lipman et al., 2006)