New charts will need to be made for future navigation. The changes in sea levels were not confined to the immediate centre of volcanic activity, but extended as far north as Porto Rico, and it was believed that the seismic wave would be found to have altered the ocean bed round Jamaica. Vessels plying between St. Thomas, Martinique, St. Lucia and other islands found it necessary to heave the lead while many miles at sea.
It is estimated that the sea had encroached from ten feet to two miles along the coast of St. Vincent near Georgetown, and that a section on the north of the island had dropped into the sea. Soundings showed seven fathoms where before the eruption there were thirty-six fathoms of water. Vessels that endeavored to approach St. Vincent toward the north reported that it was impossible to get nearer than eight miles to the scene of the catastrophe, and that at that distance the ocean was seriously perturbed as from a submarine volcano, boiling and hissing continually.
In this connection the remarkable experience reported by the officers of the Danish steamship Nordby, on the day preceding the eruption, is of much interest, as seeming to show great convulsions of the sea bottom at a point several hundred miles from Martinique. The following is the story told by Captain Eric Lillien-skjold:
“On May 5th,” the captain said, “we touched at St. Michael’s for water. We had had an easy voyage from Girgenti, in Sicily, and we wanted to finish an easy run here. We left St. Michael’s on the same day. Nothing worth while talking about occurred until two days afterward—Wednesday, May 7th.
“We were plodding along slowly that day. About noon I took the bridge to make an observation. It seemed to be hotter than ordinary. I shed my coat and vest and got into what little shade there was. As I worked it grew hotter and hotter. I didn’t know what to make of it. Along about 2 o’clock in the afternoon it was so hot that all hands got to talking about it. We reckoned that something queer was coming off, but none of us could explain what it was. You could almost see the pitch softening in the seams.
“Then, as quick as you could toss a biscuit over its rail, the Nordby dropped—regularly dropped—three or four feet down into the sea. No sooner did it do this than big waves, that looked like they were coming from all directions at once, began to smash against our sides. This was queerer yet, because the water a minute before was as smooth as I ever saw it. I had all hands piped on deck and we battened down everything loose to make ready for a storm. And we got it all right—the strangest storm you ever heard tell of.
“There was something wrong with the sun that afternoon. It grew red and then dark red and then, about a quarter after 2, it went out of sight altogether. The day got so dark that you couldn’t see half a ship’s length ahead of you. We got our lamps going, and put on our oilskins, ready for a hurricane. All of a sudden there came a sheet of lightning that showed up the whole tumbling sea for miles and miles. We sort of ducked, expecting an awful crash of thunder, but it didn’t come. There was no sound except the big waves pounding against our sides. There wasn’t a breath of wind.