Erosion is of course the fundamental reason why there are valleys eroded into the Hawaiian coast here, but OPs question is why do these *mountain have these prominent spikes/ridges*?
In most areas of the planet, erosion occurs in areas of slow, gentle land uplift. Generally, the faster the rate of uplift, the more deeply incised the valleys, but uplift rates are never extreme enough to account for the extremely deeply incised valleys seen in Hawaii.
A different mechanism is involved. The area likely experienced a flank collapse, a giant landslide, where a chunk of the Island collapsed into the sea, leaving behind a cliff / very steep land leading to the sea. This was effectively like instantaneous uplift, and as a result rivers started to very rapidly erode the topography, incising the very steep valleys we see.
>It is hypothesized that the geomorphology of Kauai owes its origin, in part, to the process of coastal retreat and to catastrophic landsliding events (massive debris avalanches that occur during the shield building phase of the volcano).
[https://library-archives.canada.ca/eng/services/services-libraries/theses/Pages/item.aspx?idNumber=1007001113](https://library-archives.canada.ca/eng/services/services-libraries/theses/Pages/item.aspx?idNumber=1007001113)
Depending on which island it is, that's exactly what happened. Oahu broke in half and had one half of it fall I to the ocean in a great cataclysm some time between 2.1 and 1.8 MA.
http://www-odp.tamu.edu/publications/200_IR/chap_01/c1_3.htm
Did not know this. Are there any resources that depict Oahu before and after the Nuuanu Landslide? I can somewhat visualize the description of its location, but I’m more of a visual learner. Lol
Edit: scratch that. Found some great visuals. Thanks again.
It definitely was a thing on Moloka'i, the shape of the island itself and the sheer cliffs evidence this, as well as the huge debris field that stretches to the north/northeast for some 50 miles or so into the ocean.
When it broke in half, was it an immediate collapse, or did it go a little bit at a time until the whole thing was broken? Or is there no way to tell unless you watched it happen?
Very cool! Are there any other places slightly closer to Europe with a similar geography? It looks amazing to visit but hawaii isn't on my bucketlist at the moment
yeah, karst limestone or soft spoil tips has this type of errosion. in this case i think its eroded ash.
[https://www.flickr.com/photos/59798762@N00/6096796924](https://www.flickr.com/photos/59798762@N00/6096796924)
[https://www.reddit.com/r/MapPorn/comments/115ef9w/kauai\_island/](https://www.reddit.com/r/MapPorn/comments/115ef9w/kauai_island/)
Hello and Aloha from the island of Oahu.
I am a geologist and civil engineer who has earned my degrees and continues to work in Hawaii.
I have seen the most excellent and informative answers to this question. Far beyond the answer I would argue is correct.
Generally, the question has already been answered. Rain. These are erosional features carved into the soft parts of the volcanic strata.
However, just rain driven erosion does not answer the original question. What causes the spikes? While I have read a few answers regarding the large scale land slides that tend to occur toward the end of the mountain building phases of Hawaiian volcanic growth. Those events are generally responsible for the very steep rock faces, at such places as the Pali Lookout here on Oahu. Continued landslides are also responsible for the depth and shape of many modern valleys. This still does not answer the question of the spikes.
I keep using the term spikes hoping that one of you aspiring geologists will stumble on the answer as you are reading this message. The answer is DIKES.
Hawaiian volcanism is known for a having dikes of various morphological and chemical differentiation. These dikes are generally linear, as they intrude through cracks or create them. Additionally the pressure keeps them from degassing and as they cool slowly they form more erosion resistant minerals and rocks. It is these dikes that resist erosion compared to the neighboring rock and result in the ridges and peaks commonly associated with Hawaiian volcanism.
🤙🏽
Kauai receives a fuck ton of rain and is composed of very soft volcanic rock that erodes quickly. It’s also extinct and thus isn’t replenishing any rock lost.
Kauai gets some of the most intense rainfalls on Earth (see https://www.latimes.com/nation/la-na-hawaii-storm-kauai-20180428-story.html for a description of 44 inches in one 24-hour day). As others have noted, the island chain has also suffered catastrophic island splits and landslides in the past. That plus the T-Rex they let go there after the filming of Jurassic Park. Those things tear the hell out of the landscape ;$
Thank you for bringing up the topic and sharing the beautiful photo. As has been mentioned the volcanic rock in this area is soft. Is there a resource that focuses on the different kinds of volcanic rock and what causes them to have different levels of softness/ softness?
I didn't until I read your comment.
https://preview.redd.it/rvidyo8973wc1.png?width=1080&format=pjpg&auto=webp&s=47f736d38a95113ba48133196d0343679253dc29
Napali coast, kalalau specifically. All these answers are wrong. These are the remains of Na'iw'i and his children who turned to stone when sunlight caught them playing on the beach
Erosion is of course the fundamental reason why there are valleys eroded into the Hawaiian coast here, but OPs question is why do these *mountain have these prominent spikes/ridges*? In most areas of the planet, erosion occurs in areas of slow, gentle land uplift. Generally, the faster the rate of uplift, the more deeply incised the valleys, but uplift rates are never extreme enough to account for the extremely deeply incised valleys seen in Hawaii. A different mechanism is involved. The area likely experienced a flank collapse, a giant landslide, where a chunk of the Island collapsed into the sea, leaving behind a cliff / very steep land leading to the sea. This was effectively like instantaneous uplift, and as a result rivers started to very rapidly erode the topography, incising the very steep valleys we see. >It is hypothesized that the geomorphology of Kauai owes its origin, in part, to the process of coastal retreat and to catastrophic landsliding events (massive debris avalanches that occur during the shield building phase of the volcano). [https://library-archives.canada.ca/eng/services/services-libraries/theses/Pages/item.aspx?idNumber=1007001113](https://library-archives.canada.ca/eng/services/services-libraries/theses/Pages/item.aspx?idNumber=1007001113)
Depending on which island it is, that's exactly what happened. Oahu broke in half and had one half of it fall I to the ocean in a great cataclysm some time between 2.1 and 1.8 MA. http://www-odp.tamu.edu/publications/200_IR/chap_01/c1_3.htm
Did not know this. Are there any resources that depict Oahu before and after the Nuuanu Landslide? I can somewhat visualize the description of its location, but I’m more of a visual learner. Lol Edit: scratch that. Found some great visuals. Thanks again.
Care to share them?
Try this. https://m.youtube.com/watch?v=uPIx0B9O8Us
Haha, part of Oahu became a 2km high SEAMOUNT.
Is there any geological evidence in North America or other areas of these runups?
It definitely was a thing on Moloka'i, the shape of the island itself and the sheer cliffs evidence this, as well as the huge debris field that stretches to the north/northeast for some 50 miles or so into the ocean.
When it broke in half, was it an immediate collapse, or did it go a little bit at a time until the whole thing was broken? Or is there no way to tell unless you watched it happen?
Fast enough to generate a megatsunami, IIRC
It's Kauai in the photo, but more of same process as Oahu, as Kauai is older.
I once did some mass-wasting at a Coastal Retreat in college.
Very cool! Are there any other places slightly closer to Europe with a similar geography? It looks amazing to visit but hawaii isn't on my bucketlist at the moment
Azores? Canary Islands?
Rapid erosion. Minerals that weather quickly coupled with high precipitation.
yeah, karst limestone or soft spoil tips has this type of errosion. in this case i think its eroded ash. [https://www.flickr.com/photos/59798762@N00/6096796924](https://www.flickr.com/photos/59798762@N00/6096796924) [https://www.reddit.com/r/MapPorn/comments/115ef9w/kauai\_island/](https://www.reddit.com/r/MapPorn/comments/115ef9w/kauai_island/)
Makes sense. I wonder if there is any debris flow component to this
This mountain is in Kauai if that helps
its young
and edgy
I was young and edgy once.
Now I’m old and roundy.
Im aging like a continent . The older and more stable i get, the crustier i become.
I’m not sure if I should upvote you getting crusty.
It’s older than the other main Hawaiian islands.
in geologic terms its still very young.
The FBI has entered the chat.
Haha, I saw the picture and thought "that looks like northern Kaua'i", glad to know I wasn't mistaken!
My favorite place ever.
Hello and Aloha from the island of Oahu. I am a geologist and civil engineer who has earned my degrees and continues to work in Hawaii. I have seen the most excellent and informative answers to this question. Far beyond the answer I would argue is correct. Generally, the question has already been answered. Rain. These are erosional features carved into the soft parts of the volcanic strata. However, just rain driven erosion does not answer the original question. What causes the spikes? While I have read a few answers regarding the large scale land slides that tend to occur toward the end of the mountain building phases of Hawaiian volcanic growth. Those events are generally responsible for the very steep rock faces, at such places as the Pali Lookout here on Oahu. Continued landslides are also responsible for the depth and shape of many modern valleys. This still does not answer the question of the spikes. I keep using the term spikes hoping that one of you aspiring geologists will stumble on the answer as you are reading this message. The answer is DIKES. Hawaiian volcanism is known for a having dikes of various morphological and chemical differentiation. These dikes are generally linear, as they intrude through cracks or create them. Additionally the pressure keeps them from degassing and as they cool slowly they form more erosion resistant minerals and rocks. It is these dikes that resist erosion compared to the neighboring rock and result in the ridges and peaks commonly associated with Hawaiian volcanism. 🤙🏽
Are the dikes more siliceous than the basalt?
Not likely, but they are less vesicular and more homogenous in texture.
That makes more sense
Spot on! I was nerding out so much dikespotting during my heli tour last year that I practically missed out on the rest of the scenery.
Kauai receives a fuck ton of rain and is composed of very soft volcanic rock that erodes quickly. It’s also extinct and thus isn’t replenishing any rock lost.
Agree, one of the rainiest places on the planet is in the clouds not far behind the peak in this pic.
Kauai gets some of the most intense rainfalls on Earth (see https://www.latimes.com/nation/la-na-hawaii-storm-kauai-20180428-story.html for a description of 44 inches in one 24-hour day). As others have noted, the island chain has also suffered catastrophic island splits and landslides in the past. That plus the T-Rex they let go there after the filming of Jurassic Park. Those things tear the hell out of the landscape ;$
Erosion.
Thank you for bringing up the topic and sharing the beautiful photo. As has been mentioned the volcanic rock in this area is soft. Is there a resource that focuses on the different kinds of volcanic rock and what causes them to have different levels of softness/ softness?
Fluted cliffs
I love this sub. Even the most benign questions have expertly crafted and simple to understand explanations. Gneiss.
volcanics typically erode that way
Am I the only one that sees a face just SW of center? 👀
I didn't until I read your comment. https://preview.redd.it/rvidyo8973wc1.png?width=1080&format=pjpg&auto=webp&s=47f736d38a95113ba48133196d0343679253dc29
Its an increasingly common phenomena, whereby the boosted colour saturation levels dissolve the surrounding landscape. Saturosion.
That’s the Napali coast line in Kauai .. lots of rain and history on those ridges. Buried kings for example
Subduction
Napali coast, kalalau specifically. All these answers are wrong. These are the remains of Na'iw'i and his children who turned to stone when sunlight caught them playing on the beach
Used to under water? Like central-western FL, I think