Edit: Sorry I think I misunderstood your question. I thought you were asking if there was any difference between the way it was written in hiragana and the kanji.
Yes, I think it is for emphasis because the hot water coming out of the power plant is much hotter than the hot water in the onsen. I read they actually use heat exchangers to lower the temperature of the water before it goes into the onsen.
P70, this one was pretty tricky, especially the last two sentences, but here is my attempt.
この おんせんが できた りゆうは 少し かわっています。
This hot spring was built for a slightly unusual reason.
この 近くに、地下の ねつを 利用して、電気を つくる 発電所が あります。
In this area there are power plants that use the underground heat to produce electricity.
発電の ときに 出る たくさんの あつい おゆを すてずに ためて、入る ことが できるように したのが この おんせんなのです。
At moment of electricity generation, plenty of hot water that comes out is stored without discarding, in order to be able to enter below the hot spring.
そのままだと おんどが 七十どを こえるので、三十八どくらいまで 下げています。
As it is, the temperature will go beyond seventy degrees, for this reason it is lowered to about thirty eight degrees.
入る ことが できるように したのが このおんせんなのです。
入る= to enter; to go into
ことが できる= to be able (to); to be possible (to)
ようにする=(following a verb) to be sure to; to do (something) so that …; to make sure to
I think this can be translated as “make sure it’s possible for (people) to enter”
It’s all nominalized with の.
Edit again: When electricity is being generated and lots of hot water that goes out is stored without being discarded, it is this hot springs that makes it possible (for people) to enter.
Page 71:
入る ときは、みんな 水ぎを きます。
When it’s time to enter, everyone goes to swim
アイスランドには おんせんが 多く あります。
In Iceland there are many onsets.
その 中でも ブルーラグーンは、 せかいじゅうから かん光きゃくが おとずれる、人気の おんせんしみつです。
The Blue Lagoon above all, visited by guests around the world, it’s a popular onsen spot
Not sure what しみつです means…
btw, it’s not necessary to say it’s “honorable.” There are certain words that are just almost always said with お in front, and others where it’s so much part of the word that you can’t remove it without changing the meaning.
Just ゆ without the お would probably be a little surprising for most Japanese people.
Looks like you have a typo, should be おんせんしせつです. I translated しせつ as facility.
So for page 71 I ended up with:
入る ときは、みんな 水ぎを きます。
When it’s time to enter, everyone wears swimming costumes.
アイスランドには おんせんが 多く ありますが、その 中でも ブルーラグーンは、せかい中から かん光きゃくが おとずれる、人気の おんせんしせつです。
In Iceland, there are many hotsprings, in particular Blue Lagoon, they are visited by sightseeing tourists from around the world, they are popular facilities.
Image Caption
まるで みずうみのような ブルーラグーン。
A lake that is quite similar to Blue Lagoon.
Got it!
And also the swimming suit!! I was lost there.
Regarding WK it should be 水着… 
I think it might be the other way. The Blue Lagoon quite like a lake
HAPPY NEW YEAR’S EVERYONE!
We don’t get pronouns in Japanese to help us know whether the translation is “it is visited” (just blue lagoon) or “they are visited” (the many Icelandic onsen).
But does the sentence structure tell us which the meaning is? せかい中から かん光きゃくが おとずれる follows the clause contains は, so does that mark Blue Lagoon as the main topic of the sentence, and therefore the topic of the last two clauses?
Happy new year everyone! Hope you will be enjoying a 忘年会 tonight!!
I agree with you
I think "In Iceland” is the topic of the first clause and “Blue Lagoon” is the topic of the second clause. It’s also possible that one of the は’s could be a contrastive marker.
But in either case, you can tell from the sentence structure that せかい中から かん光きゃくが おとずれる refers to the Blue Lagoon (and not to to the many onsens in Iceland) because not only is it in the second clause but it is also a relative clause of しせつ.
So I think this sentence can be translated as,
There are many onsens in Iceland but the Blue Lagoon, above all, is a popular onsen facility where tourists throughout the world visit.
Ah okay, thanks for this. Longer sentences trip me up sometimes.
Page 72:
パンダが 有名に なった、いがいな きっかけって？
Is it true that the Pandas became famous unexpectedly?
白と 黒の 体の もようと、あいらしい しぐさで、せかいじゅうで 大人気の どうぶつと いえば、パンダです。
With a white and black body pattern and an adorable behavior, Pandas are an animal very popular around the world Not sure about いえば
今では 中国を だいひょうする どうぶつです。
Nowadays, it’s the animal that represents China
長い あいだ、 中国の 山おくに すむ 人びとにしか、その すがたは 知られて いませんでした。
For a long time, nothing but people lived in deep in the mountains of China, that form was not known ?? I’m missing something here. I have the feeling it says completely the opposite.
Maybe:
For a long time they lived deep in the mountains of China without any people、their appearance was not know.
しか…ない is “except” or “only,” depending on how you want to frame the verb as positive or negative.
I’m still not sure how to translate it…
For a long time only people who lived in the deep mountains of China knew what they looked like.
Or
For a long time, their appearance was known to no one except for those living deep in the mountains of China.
etc.
Ahhhh!!! Got it!! Now it makes sense
Thank you Leebo先生 
Thanks so much @Leebo I was having trouble with that sentence as well. 
My initial translation of it was a total mess haha. 
Can anyone explain the きっかけって at the end of this sentence please?
Is it:
切っ掛け(きっかけ):chance; start; cue; excuse; motive; impetus; occasion
and って: tte - Jisho.org
??