A prophecy attributed to St. Hildegard of Bingen is perhaps the most famous prophecy of a nation being destroyed by tidal waves in private revelation:
Before the comet comes, many nations, the good excepted, will be scourged by want and famine. The great nation in the ocean that is inhabited by people of different tribes and descent will be devastated by earthquake, storm, and tidal wave. It will be divided and, in great part submerged. That nation will also have many misfortunes at sea and lose its colonies. [After the] great comet, the great nation will be devastated by earthquakes, storms and great waves of water, causing much want and plagues. All coastal cities will live in fear, and many of them will be destroyed by tidal waves, and most living creatures will be killed, and even those who escape will die from horrible diseases. For in none of those cities does a person live according to the laws of God.
We should note however that this prediction is most likely of far later origin than St. Hildegard. This prophecy is widely circulated on the internet due to its inclusion by popular books on Catholic prophecy (such as those by Yves Dupont), but there are no solid references in any of these works to the original source of this prophecy amongst St. Hildegard’s vast collection of writings. St. Hildegard was a prolific writer, and her works (which include 9 books and over one hundred letters, as well as 70 poems and 72 songs) have been studied extensively by modern historians. The fact that none of these works are referenced amongst the various websites and books which quote the above prophecy should send alarm bells ringing.
There were many prophecies falsely attributed to St. Hildegard during the later Middle Ages, such as those issued by the anti-mendicant movement. Given the lack of reference to the original source and the inclusion of some anachronistic language, it is likely that the above prophecy is one of these later pseudonymous writings.
This leads us to question whether a pseudonymous prophecy can still offer genuine insight into the future. The Catholic Church teaches that anyone can be recipients of genuine prophecy, regardless of their background - either through interior spiritual vision, or through contact with angelic or demonic forces. Pope Benedict XIV summed up this position in his work Heroic Virtue: On the Beatification and Canonization of the Servants of God:
“The recipients of prophecy may be angels, devils, men, women, children, heathens, or gentiles; nor is it necessary that a man should be gifted with any particular disposition in order to receive the light of prophecy provided his intellect and senses be adapted for making manifest the things which God reveals to him. Though moral goodness is most profitable to a prophet, yet it is not necessary in order to obtain the gift of prophecy.”
We must also take into consideration the fact that the use of pseudonyms to link prophecies to illustrious figures from the past was commonplace in apocalyptic literature from its very inception. The Ethopic and Slavonic Books of Enoch are perhaps the best example of this convention, since we can be certain that these writings did not originate with the antediluvian prophet of Gen 5:24. The tradition of naming prophetic texts after heroic figures of the past can also be found in various other apocalyptic and extra-biblical writings - a collection of works known as the pseudepigraphia. In fact the Book of Revelation is noted for being one of the only instances in apocalyptic literature which does not follow this custom. The author instead gives his own name - John.
The use of a pseudonym to attribute mystical writings to noted authorities from the past was employed to gain immediate recognition for the work at hand, rather than relying on the (perhaps non-existent) reputation of the seers themselves. It was also a way of retaining anonymity and dedicating the work to figures of particular inspiration to the writer. So although the above prophecy drops a considerable amount of prestige regarding its provenance, whether or not it is a genuine oracle of St. Hildegard should not detract from the inherent prophetic ability it may still possess.