An interim note for AW#45

This is a quick note for AW#45.

Up to now, I have received 18 contributions for the AW#45 “Geological Pilgrimage”. Thank you! As far as I know, at least one post is still on its way (that is mine one :P). So, there will be still time to send in yours before the end of this week. I shall then have a summary post.


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Most Important Teacher – AW#44

In Chinese, we have a phase “薪火相傳”, which literally means “to pass the flame”. And  actually the phase has a deeper meaning, which is “to pass the knowledge and good traditions to the next generation”.

I am a very lucky person. I have met many good teachers in my life. Some of them not only passed on their knowledge, but had also influenced the way I see the world, and helped me to become the person I am today. But, when Simon of metageologist asked us who is our most important teacher,  I know immediately who is the most important teacher of mine.

Of all the good teachers I have had, Prof. LS Chan at the HKU is the most important. Prof Chan is my abecedarian, the teacher who introduced me to the grande of geology. He who took me to the first geological field trip I ever had, showed me how to read a geological map, use a compass, bang on an outcrop… This is, of course, not THE reason why he is special.

Prof Chan is truely supportive to his students. I could not easily explain how supportive he was when I was doing my Master under his supervision and he is still doing so to me. He once told me a short conversation he had with his own professor when he just finished his PhD (some 30 years? ago). He asked his professor, “Professor, you have done so much for me, … How am I gonna repay you?”, and Professor replied, “If you wanna repay me, all you need to do is to do exactly what I have done to you to your own students in the future.”

I know these are not the exact wordings.  But this is what “薪火相傳” means.

This post is the Accretionary Wedge #44, hosted by Simon Wellings. And this is not exactly a post about geology.

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AW#45 Geological Pilgrimage – Call for Posts

I am happy to host the 4645th Accretionary Wedge geoscience blog carnival. The topic I have chosen is:

Geological Pilgrimage – the sacred geological place that you must visit at least once in your lifetime 

Because the topic may slightly overlap the previous AW#16 – Geologists’t List, I would like to define the pilgrimage as a single place, which is “geologically” unique,  relatively remote, and requires some difficulty to get to.  If you have already done your geological pilgrimage, please share with us your experience. If you are still planning your pilgrimage, then let us know where your sacred geological spot is and why.

Please post a link of your post in the comment below, or via Twitter @denisetang). The due date for handing in is 30th April 2012, but you will definitely get a couple of extra days (or a week) before a summary is posted.


(Oops…I got the number wrong. It should be Accretionary Wedge #45.)
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Most Memorable Geological Event – AW#41

The most memorable geological event that I had directly experienced occurred when I was at the final year of my undergrad. It was a rockfall – a man-induced one.

My final year thesis was to investigate the geological strucutures in a Permian sedimentary unit in Hong Kong. The unit exposes only at the coastal section of a small isolated island which is connected to the mainland by a tomobolo. My project was to measure the orientations of the folded layers and determine the folding patterns, deformation phases etc.

On one particular field day, I invited my best friend and classmate, Brandon, to assist my field work. So, we walked along the coastal section, making records and measurements of the geological structures along the way. And then, we arrived at an outcrop which was essentially a cliff. Some sub vertically dipping rock layers were nicely seen, but we would need to make a 1-2m climb on the rock face to reach the point where we could make a good measurement. Brandon was a stubby young man then, had kindly offered to help me to do the measurement, when I could stay on the ground and record the strike and dip.

Somehow, we were young, inexperienced and probably too careless. We had not judged the conditions before acting. Brandon climbed up the rock face with one of his hands holding a geological compass. He probably did not realise that he was holding onto a rather loose boulder in one of his moves. All of a sudden, the boulder moved and toppled. It hit Brandon’s chest, and bonunced. Brandon fell with the boulder and I was just beneath them at the toe of the slope.

Although it was probably not a life threatening event, but it was quite scary. The boulder was blocky, about half a metre in diameter, and Brandon was over 150 or 160 pounds. They fell just next to me. It was certainly a near miss. Luckily, Brandon did not get serious hurt, but minor bruise.

What was the lesson learnt? Well, for me, never stay too close below a cliff when someone is climbing. And for Brandon, never trust a rock outcrop, it may not be able to support his own weight. OK, seriously, the lesson learnt was the importance of safety when doing fieldwork. Even a minor mistake, or a misjudgement, or carelessness, may result in  serious consequence. Looking back after more than 13 years, I still believe that I was very lucky.

This post is in response to the Accretionary Wedge #41, hosted by Ron Schott.

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Holiday Geology Picture (3): Permafrost, Northern Xinjiang, China

Happy holiday! Well, today is the last day of the 4-day-long Christmas holiday in Hong Kong. Many of us will have to go back to work tomorrow…So, I am trying my best to enjoy myself.

I have chosen a picture of my year-2005 trip to Xinjiang for today’s “Holiday Geology Picture”. The trip was a kind of adventure, because I was on horse-back for 4 days with three other friends to visit some remote places in northern Xinjiang. The places were so remote that there was no proper accommodation and we had to stay with the nomads at night. We rode across grasslands and valleys, and visited small isolated villages.

On one of the days, we crossed a saddle where the permafrost was melting. It was a pity that we did not bring our GPS with us, and I could not recall the exact location of this place. It was close to the county of Altai at the northern tip of Xinjiang. We rode passed many small lakes formed by the melting permafrost and enjoyed the views of mountain chains. The place was beautiful, part of it was because the place was so peaceful.

The trip was very memorable, because there was an accident on the final day of our horse-riding. The horses walked leisurely for most of the time of the trip. But, suddenly they all got mad and started to run. I was lucky because I managed to control my horse before it ran too fast. But for my friends, they just couldn’t stop the horses. I could see that they got thrown down from the horse back one by one. Almost unbelievably, they got only minor scratches…

This is a picture of us riding happily before the accident.

More “Holiday Geology Pictures” can be found here and here.

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Holiday Geology Picture (2): Yardang, Gansu, NW China

Happy Boxing Day! I am continuing my Holiday Geology Picture series. The geology picture I have here is from Mainland China.

This is a landscape called “Yardang” in Chinese. It means a series of small mounds formed by wind erosion. The picture was taken in 2004 when I visited the most easily accessible part of the Silkroad in northwest China. I traveled from Gansu Province to Xinjiang Province for more than 2 weeks. The site is close to Dunhuang and now is a national geopark in China.

I could not remember now the details of the rock formation. If my memory is correct, they are sandstones that formed in the mid-Pleistocene.

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Holiday Geology Picture: Mt Showa Shinzan, Hokkaido

Last week, Evelyn of Georneys posted a series of geology pictures for the geology picture-a-day week.  Some other geobloggers also shared some very interesting geology pictures.

Well, I must confess that I am a SLOW person, and could not catch up with the speed of the geoblogsphere. So, my geology picture meme comes a little bit late. And I am calling this series “Holiday Geology Picture” because the pictures I am going to share here were taken while I was on holiday, and they are posted on “holiday”.

The first picture is Mt Showa Shinzan, Hokkaido, Japan (taken in Oct 2010). It is a young volcanic  dome formed between 1943 and 1945.

There was a display panel describing the volcano:

“A series of violent earthquakes, sometimes over 200 large tremors in one day, occurred from December 1943 until April 1944. The result was the transformation of wheat fields into a raised plateau 50 m high. The first volcanic eruptions started on June 23, 1944, from one crater and continued for four months, destroying the wheat fields, houses and railroads. As a result, this area turned into the egg-shaped plateau, 300 m above sea
level. And seven crater were founded [sic]. In November 1994, lava started rising from the central crater and continued unitl September 1945. At last, the altitude was 407 m. But smoke is still spouting from the reddish-brown peak, which instantly recognisable by its unique pyramid shape.
Because Mt Showa Shinzan was born at the end of the WWII, the military kept this fact a secret. So, satistactory investigation couldn’t be done. Under this situation, Mr. Masao Mimatsu (1888-1977), the postmaster of the district, investigated the development of Mt. Showa Shinzan in detail. His records are valuable scientific data to analyse these unique volcanic activities.”

This is the development record of the volcanic dome drawn by Mr. Mimatsu.

And, Happy Holiday!

Posted in Geology, Japan, volcano | 1 Comment

Back to School – AW#38

This month’s Accretionary Wedge topic is “Back to School”, hosted by Anne Jefferson.

Anne has asked us to share “about the things that we don’t often learn or teach in school but that may turn out to be quite important in the real world” as geology students / professors / professionals / enthusiasts.

I have got deep reflections on the topic, not only as a geologist practicing outside the academia, but also as a student who is still attending a post-grad school. There are so many things that we should have learnt, or qualities or personality to be developed. My boss always says that he wish his subordinates to “be passionate about the subject (geology)” and “be creative” or “love to do fieldwork” etc.. These are all true, but I would like to share here two things that, I believe, are important.

The first quality is daring to challenge to old school of thoughts. Students or scholars from the western world may find it quite common to challenge their bosses or supervisors. However, in the Chinese culture, we are not accustomed to dispute with someone who is more senior or more experienced, or to question ideas which were established by some old, emeritus  professors. Daring to challenge others, and be able to defend your own idea, to me, is a paramount important thing here.

I have learnt my lesson when I was doing my MPhil back in 2003. My research topic was a controversial issue over the origin of a rock unit. After three years of investigation, I came up with an interpretation which basically disagree with what a well-respected and experienced geologist has believed. So, I put my findings and interpretation in my thesis. But I was not brave enough at that time to publicly defend my own idea. Looking back, I regret this a lot. Because some unhappy events subsequently occurred, which could have been prevented.

The second important thing is “always be prepared to learn new thing“. To be honest, I always think that I have not learnt enough about geology. Sometimes, I just feel I know so little, that makes me very anxious. The reason is partly because geology is such a broad subject, and new ideas come up everyday. The truth is, we always have new things to learn in geology. This is why this subject is so exciting and fun. Passion is the driving force, but getting ready to be a life-long learner is also needed. This is also to do with getting ready to accept new challenges.  So, I have not stopped learning yet, not until the end of my day.

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Kinky Columns


I was inspired by Callan’s interesting post last week on the patterns of some cooling columns.  Callan has explained, using some nice illustrations, the concept that the cooling joints are formed perpendicular to the cooling front (or thermal gradient), and that some curved columns can be described as a result of corrugated cooling front.

But then, I asked myself, how can I explain the kinky columns found here in Hong Kong? Can they be explained by the presence of wavy cooling front as well?

The kinky columns are well exposed on an old quarry face near a reservoir in southeast Hong Kong. The entire rock face is over 30 m in height. The diameter of individual columns here is about 1.2 m. The entire unit has been tilted at 20-30 degrees to the east (as shown by the consistently inclined long-axis of the columns).

I focused on the kinky columns exposed on the middle part of the rock face, and tried to draw the possible cooling fronts. The pattern of the cooling fronts will be somewhat like this.

It seems that some cooling fronts are converging while others are diverging. Does it make sense? I cannot easily think of a reason for the waviness of the cooling fronts.

Another good exposure is found not far away. Similarly, I tried to mark the cooling front on the picture.

Again, the cooling fronts seems to be wavy. In the middle of the photos, the kinky columns are intruded by a mafic dyke. However, the mafic dyke does not seem to have affected the cooling pattern and the formation of the cooling joints. It is apparent that the intrusion post-dated the formation of cooling columns, although the time gap between these two events is uncertain.

So far so good, right?

But there is a major issue. If you look at the first picture again, you will see that the kinking is actually not restricted to a single kink-band. There are multiple kink-bands, occurring repeatedly and are sub-parallel to each other. They extends for several hundreds of metres, although no conjugate sets are found. This kind of kinky pattern is also seen at other parts of the same tuff unit.

So, if we are trying to explain the kink bands as the products of wavy cooling fronts, then this would suggest that the same wavy pattern of the cooling front should have repeated again and again at different position in the cooling unit. I doubt how this could have happened. Alternatively, the kink-bands could be the result of tectonic movement. However, as I have said, no conjugate sets are found. So, this explanation is questionable.

The one explanation we have used to use: the kink-bands could have formed by slump folding when the cooling unit was still “semi-solidified” and able to deform in a “plastic manner”.  The columns might have bent towards the same orientation during the tilting of cooling tuff unit, probably under its own weight, to form the kink-bands (as a kind of slump folding?). This seems to be a better explanation. However, one issue remains: how can the cooling columns (and the tuff unit) on one hand “deform in a plastic manner”, but on the other hand formed the kink-bands, which is essentially a brittle deformation??

Anyone have any clues?


Posted in Geology, Hong Kong | 1 Comment

My Favourite Geology Word AW#35

This is my first time joining the Accretionary Wedge Geoscience Blog Carnival. The current topic for AW#35 is “What is your favourite geology word?” (hosted by Georneys).

My favourite geology word is this one — MYLONITE

Definition: A fault rock which is cohesive and characterised by a well developed schistosity resulting from tectonic reduction of grain size, and commonly containing rounded porphyroclasts and lithic fragments of similar compositions to minerals in the matrix. Fine scale layering and an associated mineral of stretching lineation are commonly present. Brittle deformation of some minerals may be present, but deformation is commonly by crystal plasticity. (source)

Back in 2000, when I was just starting my career as a geologist, I was assigned to carry out a petrographic study of dynamically metamorphosed rocks in northwest Hong Kong. This was when I first got to understand this word – MYLONITE.  In Chinese, the word is translated to 糜稜岩 (Míléngyáng). I actually think that this is the most ‘beautifully’ translated geology word in Chinese.

I have some pictures of mylonite from Hong Kong.

This is a mylonite outcrop. The protolith (parent rock before deformation) is a pebbly quartz sandstone. Several years ago, I wrote a short ‘poem’ describing this outcrop.



(Even strong rock can be twisted and deformed.)

The dynamic metamorphic zone in northwest Hong Kong is quite wide. Therefore, the metamorphism has affected not only the sedimentary rocks, but also some granites and volcanic rocks in the region.

This is a hand specimen of mylonitic granite. The porphyroclasts of quartz set in very fine-grained, dynamically recrystallised matrix, showing clear foliation.

This is a mylonitic volcanic rocks under microscope.

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