This was their final day in the city, and all the participants in the Congo expedition described a similar reaction: the city, which had been so mysterious before, was somehow stripped of its mystery. On this morning, they saw the city for what it was: a cluster of crumbling old buildings in a hot stinking uncomfortable jungle.
They all found it tedious, except for Munro. Munro was worried.
Elliot was bored, talking about verbalizations and why he wanted tape recordings, and whether it was possible to preserve a brain from one of the apes to take back with them. It seemed there was some academic debate about where language came from; people used to think language was a development of animal cries, but now they knew that animal barks and cries were controlled by the limbic system of the brain, and that real language came from some other part of the brain called Broca's area. . . . Munro couldn't pay attention. He kept listening to the distant rumbling of Mukenko.
Munro had firsthand experience with volcanoes; he had been in the Congo in 1968, when Mbuti, another of the Vi?runga volcanoes, erupted. When he had heard the sharp explosions the day before, he had recognized them as bromides, the unexplained accompaniments of coming earthquakes. Munro had assumed that Mukenko would soon erupt, and when he had seen the flickering laser beam the night before, he had known there was new rumbling activity on the upper slopes of the volcano.
Munro knew that volcanoes were unpredictable - as witnessed by the fact that this ruined city at the base of an active volcano had been untouched after more than five hundred years. There were recent lava fields on the mountain slopes above, and others a few miles to the south, but the city itself was spared. This in itself was not so remarkable - the configuration of Mukenko was such that most eruptions occurred on the gentle south slopes. But it did not mean that they were now in any less danger. The unpredictability of volcanic eruptions meant that they could become life-threatening in a matter of minutes. The danger was not from lava, which rarely flowed faster than a man could walk; it would take hours for lava to flow down from Mukenko's summit. The real danger from volcanic eruptions was ash and gas.
Just as most people killed by fires actually died from smoke inhalation, most deaths from volcanoes were caused by asphyxiation from dust and carbon monoxide. Volcanic gases were heavier than air, the Lost City of Zinj, located in a valley, could be filled in minutes with a heavy, poisonous atmosphere, should Mukenko discharge a large quantity of gas.
The question was how rapidly Mukenko was building toward a major eruptive phase. That was why Munro was so interested in Amy's reactions: it was well known that primates could anticipate geological events such as earthquakes and eruptions. Munro was surprised that Elliot, babbling away about freezing gorilla brains, didn't know about that. And he was even more surprised that Ross, with her exten?sive geological knowledge, did not regard the morning ash-fall as the start of a major volcanic eruption.
Ross knew a major eruption was building. That morning, she had routinely tried to establish contact with Houston; to her surprise, the transmission keys immediately locked through. After the scrambler notations registered, she began typing in field updates, but the screen went blank, and flashed:
HUSTN STAIN OVRIDE CLR BANX.
This was an emergency signal; she had never seen it before on a field expedition. She cleared the memory banks and pushed the transmit button. There was a burst transmission delay, then the screen printed:
COMPUTR DESIGNATN MAJR ERUPIN SIGNATR MU-KENKO ADVIS LEAV SITE NOW EXPEDN JEPRDY DANGR REPET ALL LEAV SITE NOW.
Ross glanced across the campsite. Kahega was making breakfast; Amy squatted by the fire, eating a roasted banana (she had got Kahega to make special treats for her); Munro and Elliot were having coffee. Except for the black ashfall, it was a perfectly normal morning at the camp. She looked back at the screen.
MAJR ERUPTN SIGNATR MUKENKO ADVIS LEAV SITE NOW.
Ross glanced up at the smoking cone of Mukenko. The hell with it, she thought. She wanted the diamonds, and she had gone too far to quit now.
The screen blinked: PLS SIGNL REPLY.
Ross turned the transmitter off.
As the morning progressed they felt several sharp jolting earth tremors, which released clouds of dust from the crumbling buildings. The rumblings of Mukenko became more frequent. Ross paid no attention. "It just means this is elephant country," she said. That was an old geological adage: "If you're looking for elephants, go to elephant country." Elephant country meant a likely spot to find whatever minerals you were looking for. "And if you want diamonds," Ross said, shrugging, "you go to volcanoes."
The association of diamonds with volcanoes had been recognized for more than a century, but it was still poorly understood. Most theories postulated that diamonds, crystals of pure carbon, were formed in the intense heat and pressure of the upper mantle one thousand miles beneath the earth's surface. The diamonds remained inaccessible at this depth except in volcanic areas where rivers of molten magma carried them to the surface.
But this did not mean that you went to erupting volcanoes to catch diamonds being spewed out, Most diamond mines were at the site of extinct volcanoes, in fossilized cones called kimberlite pipes, named for the geological formations in Kimberley, South Africa. Virunga, near the geologically unstable Rift Valley, showed evidence of continuous volcanic activity for more than fifty million years. They were now looking for the same fossil volcanoes which the earlier inhabitants of Zinj had found.
Shortly before noon they found them, halfway up the hills east of the city - a series of excavated tunnels running into the mountain slopes of Mukenko.