Valkyrie - I thought I'd read up on the commentaries again, as I was sure I had read that geology had confirmed that mountains damped down earthquakes as per the following verse:
Al-Anbiya' Chapter 21 : Verse 31
And We have placed in the earth firm mountains lest it should quake with them; and We have made therein wide pathways, that they may be rightly guided.
However, you are right the reply you got from the geologist goes against this verse and my understanding.
So, this is what I had read
"..Geology has established the fact that mountains have, to a great extent, secured the earth against earthquakes. In the beginning the earth was very hot from the inside. When as a result of the intense heat gases were formed in the bowels of the earth, they forced a way out, thus causing violent agitations and eruptions in the forms of volcanoes, which having cooled down took the shape of mountains (..Ency Brit under 'Geology'). The verse may also signify that the mountains are a great help to the earth in moving steadily on its axis. The Quran spoke of the earth as 'moving round' long before it was discovered it was not stationary and moved on its axis and round the sun."
I also Googled - and yes there are a number of claim and counter claims out there on the subject. Some say that the 'shaking' prevention from mountains is really referring to the stability of the earth in spinning, rather than earthquakes (as in the latter part of the commentary).
I am personally not satisfied with these explanations and have to say that the Geologist's opinion that mountains do not prevent/mitigate earthquakes is not compatible with this verse.
Therefore, this verse is either scientifically incorrect or the geologist's opinion is incorrect.
[As a non-geologist though, once a mountain range has formed, I would have thought that earthquakes would subside as the 'bulging' forms a pressure valve for the tectonic plates. Using the analogy provided by the geologist (and high school geography), earthquakes happen when pressure has built up and the plates have no where to go - so with a deck of cards, there is pressure and trembling up until the cards buckle - but when they buckle, extra pressure causes a rise in the cards, but a relatively smooth rise and not the 'trembling'.
Therefore, aren't the mountains a sign of significant historical (geologically speaking) movements, and now with these in place the violent movements that caused the mountains are gone and we are left with the (geologically speaking) lighter earthquakes of today.
I mean, it goes without saying that we haven't seen a new mountain range form in the past few million years.
Therefore, perhaps the Geologist is not thinking far back enough to the earthquakes and geological movements that caused the mountain ranges to form. I'd be interested in hearing whether they agree or disagree that we have fewer earthquakes/upheavals in our current time than at the time before mountains were formed (as the Quran is saying mountains reduce earthquakes - the contention would only be wrong if mountains, or the process making mountains, had no effect on the stability of the surface of the earth)]
I also did a search on reference to mountains - some say mountains are firm, others say in the final days mountains will become like dust..
TaHa Chapter 20 : Verse 105
And they ask thee concerning the mountains. Say, 'My Lord will break them into pieces and scatter them as dust;
Al-Naml Chapter 27 : Verse 88
And thou seest the mountains, which thou thinkest to be firmly fixed, pass away as the clouds pass away - the handiwork of Allah Who has made everything perfect. Verily, He is full Aware of what you do.
Al-Kahf Chapter 18 : Verse 47
And bethink of the day when We shall remove the mountains and thou wilt see the nations of the earth march forth against one another and We shall gather them all together and shall not leave any one of them behind.
Al-Haqqah Chapter 69 : Verse 14
And the earth and the mountains are heaved up and then are crushed in a single crash, ,
Al-Muzzammil Chapter 73 : Verse 14
On the day when the earth and the mountains shall quake, and the mountains will become like crumbling sand-hills.
Al-Qari`ah Chapter 101 : Verse 5
And the mountains will be like carded wool.
Al-Nahl Chapter 16 : Verse 15
And He has placed in the earth firm mountains lest it quake with you and rivers and routes that you may find the way to your destination.
Al-Naba' Chapter 78 : Verse 7
And the mountains as pegs?
This when read in context is asking a question - v6 'Have We not made the earth as a bed, (v7) And the mountains as pegs? v8 And we created you in pairs, v9 And made your sleep for rest.
So for me, this verse is asking a question - is the earth not +as+ a bed and the mountains are (relative to the earth) pegs in it?
(Again, Google shows articles from Muslims explaining what 'pegs' mean - that mountains penetrate into the crust etc, and counter arguments that mountains are formed from tectonic plates. I think that in this verse pegs is just a juxtaposition to the previous verse which talks of the earth as a bed).
Apologies for the long post - but always happy to research Quranic verses and always amazed how much can be said about them!
Cheers,
Shafique