How did the Olive Tree survive the flood?

ויטע כרם, “he planted a vineyard.” According to Rashi, Noach had taken branches of the fig tree and the grapevine with him into the ark. (based on B’reshit Rabbah 36,3) These plants are especially sensitive to water and need protecting more than other trees.

והנה עלה זית טרף בפיה, “and here it had torn off an olive leaf with its beak.” Seeing that destruction had been decreed on man and beast there was no need for the Torah to have reported that the trees too had been doomed by the deluge. In fact, the destruction of vegetation on earth had been so thorough that our sages in Bereshit Rabbah 28,3 claim that even the lower millstones had been thoroughly destroyed. This may be based on Job 14,19 אבנים שחקו מים, “the waters wear away even stones.” There was no need for the Torah to add that the leaf which the dove carried in its beak must have been one that had withered already a long time previously. The question is: where did the dove find even such a leaf? The Midrash offers several explanations. Rabbi Levi claims that the leaf came from Mount Olives (Jerusalem), seeing the deluge had not touched the Holy Land. He claims that G-d had said to Ezekiel (Ezekiel 22, 24) בן אדם אמר לה את ארץ לא מטהרה היא לא גשמה ביום זעם, “Ben Adam, say to her: “You are a land that has not been cleansed; she had not been rained upon on the day of fury.” The words לא מטהרה refer to the fountains of the deep beneath the Holy Land not having opened at the time of the deluge, whereas the words ולא גושמה mean that no destructive rain fell on the Holy Land during the period of the deluge. Nonetheless, it is fair to assume that the waters of the deluge which had flooded neighbouring countries also spilled over into the Holy Land. After all, the Torah testifies that the waters of the deluge “covered all the high mountains beneath the whole sky (7,19).” Seeing that no rain had fallen on the Holy Land which would have uprooted and broken the trees in that land, the waters which spilled over into that land did not have such a destructive effect. It is quite plausible therefore that the dove took the leaf from Mount Olives.
This explains what is meant when the Torah wrote ((8,11) וידע נח כי קלו המים מעל הארץ, “Noach realised that the waters had subsided from upon the earth.”

"And oil from the flint of the rock": These are the olives of Gush Chalav.