ろくに and trouble understanding sentence meaning


I came across the following sentence in an exercise:

> 最近まで_____考えてもみなかったことの数々が、なだれるように頭に浮かんできた。
>
> A. ろくに、B. ようするに、C. ぶりに、D. さらに

The right answer was A.

I'm having a hard time parsing this sentence. Here are the bits that I think I
understand:

> 最近まで
>
> Until recently
>
> 考えてもみなかったこと
>
> Things that I don't see even though I ponder
>
> 頭に浮かんできた
>
> It started coming to my mind

But I really can't wrap my head around なだれるように, and the global meaning of the
sentence and how the bits are connected to each other.

Furthermore, Jisho says ろくに means "well, enough, sufficient", but I don't
really get how it fits in this sentence.

What would be a correct translation of that sentence? Also, what is the nuance
that ろくに brings in here?




> 考えてもみなかったこと  
>  Things that I don't see even though I ponder

I'm afraid you're not parsing this part correctly.  
The (～て)みなかった is a subsidiary verb meaning "didn't try doing".  
考えてみる "try thinking" + も "even" + negative ない + past た  
⇒ 考えてもみなかった _lit._ "didn't even try thinking" → "didn't even think of" "didn't
even occur to me"

ろくに is used with a negative word/phrase.  
「ろくに～～ない」 "don't ~~ enough" "hardly ~~"

So ろくに考えてもみなかった is like "I hadn't even thought of ~~ enough" "I didn't give
enough/much thought to~~"

なだれるように (雪崩れるように・傾れるように, "as if sliding down") describes how ろくに考えてもみなかったことの数々
("many of the things that I had never given much thought to") pop into your
head.

