Shen Bing looked around and said, "Lu Zhe, this should be a dormant volcano. The vegetation here is too lush - it couldn't have grown to this extent in just a few decades."
Lu Zhe put Qianqian down on a relatively clean rock and said, "The abundance and diversity of species and vegetation here exceeds the general comprehension. The key is that at the bottom of this crater-like volcano, the vegetation is growing so vigorously."
Shen Bing looked up towards the top and said, "The volcano's crater looks less than 200 meters from the bottom, but from the outside the volcano is at least 300 meters high. So the bottom of the volcano must be quite elevated, definitely higher than our campsite."
Lu Zhe smiled and said, "You're right! Looking at the volcano's cross-section, the bottom diameter and the side wall height are about the same. So when the sun's angle is between 45 and 135 degrees from the ground, the vegetation at the bottom can still get direct sunlight."
Lin Qianqian took out a notebook from her plastic bag and calculated, "Assuming the volcano sidewall height equals the diameter, and the east-west line is the diameter, any point on that diameter making a 45 degree angle with the crater means a quarter of 180 degrees.
And we're not far from the equator, so day and night lengths are about equal - a quarter of 12 hours is 3 hours. So the bottom only gets 3 hours of direct sunlight along the diameter, and even less elsewhere, with no direct sunlight in the southern and northern corners!"
Lu Zhe nodded, "You're right. Looking at how lush the vegetation is, it's clearest along the east-west diameter line. The south-north corners are also flourishing but mostly shaded plants."
Seeing Lu Zhe's somber expression, Shen Bing said regretfully, "But three hours of sunlight is still too little."
"More than just direct sunlight," Lu Zhe contemplated.
"The vegetation couldn't be so thriving with just direct sunlight. They likely rely more on indirect sunlight."
Shen Bing and Qianqian looked at each other puzzled, "Indirect sunlight?"
Lu Zhe looked up and said, "Remember the Ming dynasty writer Gu You's Xiangjuexuanji? He made four windows facing south to let sunlight in, with the wall reflecting light to brighten the room.
Qianqian said, "I remember."
Shen Bing smiled wryly, "Just vaguely."
"He opened north-facing windows but couldn't get southern sun, so he built a wall by the window to reflect light and brighten the room."
Shen Bing nodded, "True, it's past four now, yet not as dark as imagined."
Lu Zhe pointed at the inner volcano walls, "These are about 90 degrees vertical to the ground. Bird droppings can't adhere to these walls, any soil gets washed away by rain, keeping the rock exposed.
The smooth volcanic rock contains high silicon dioxide and rock crystals, reflecting some weakened sunlight and better suiting temperate fruits."
"Great!" Qianqian happily exclaimed, "But can this light enable photosynthesis?"
"Any light with blue, purple and red can promote photosynthesis, whether it's reflected, refracted or diffracted!"
Shen Bing said, "I know, the fruits and vegetables in greenhouses back home use LEDs to supplement light when lacking sunlight to increase yield."
Qianqian happily said, "That's great, we can plant fruit seeds here! When do we start?"
Lu Zhe sighed, "Not that easy! Even if soil and sunlight issues are solved, some tougher problems remain."
"What problems?"
"Firstly, monsoons - I don't know if drainage exists here. With none, the seven days of heavy rain will likely flood this place.
Secondly, with quick drainage, how do we channel water here from the sulfur springs in droughts, certainly not by bottles.
Thirdly, clearing land - the optimal planting line is the east-west diameter, but with such tall and short trees, impossible to clear land with our tools.
And fourthly, the birds provide ample fertilizer but also like eating fruits - our watermelons and strawberries would likely suffer pest damage halfway through growing."
Shen Bing nodded, understanding each issue Lu Zhe raised was a realistic problem. Without resolving them, much time and effort would be futile.
But she believed Lu Zhe could find reliable solutions in their survival days ahead.
Lu Zhe had wanted to go down to the volcano bottom but seeing the time, the sun would soon set - staying would mean spending the night there.
"Let's head back, the captain and others will worry if we're late. We can come back another day," he said.
"Okay, I'm hungry too!"
Lu Zhe carried Qianqian again as the three entered the cave to return to camp.
But upon reaching the pool, Qianqian suddenly jumped and yelled, "So hot!"
Lu Zhe noticed too - the pool temperature had risen markedly.
Previously around 40 degrees Celsius, now nearing 50 degrees at night!
Just a 10 degree difference, but Lu Zhe could barely stand it, let alone Shen Bing and Qianqian swimming through that channel.
"Why did the temperature rise so much!"
"Too hot to even soak feet!"
"Could it be...increased volcanic activity?"
Lu Zhe contemplated, "Two possibilities! One is increased volcanic activity. The other is different currents or magma flows causing varying effects at different times - see how not just temperature rose, but water levels are much higher."
Shen Bing nodded, "You mean cold currents flow below the island during the day, and warm currents at night, interacting differently with the magma."
Lu Zhe nodded, "That's the idea, though it's still conjecture! To prove it, we'd have to see if temperatures revert in the day. Otherwise..."
He trailed off grimly, "It may really be increased volcanic activity."
Qianqian worriedly asked, "What do we do now!"
Lu Zhe considered, "What can we do? Just stay here overnight, we'll think of getting back tomorrow."
"In the cave?"
Lu Zhe weighed options, "Yes, though difficult, at least it's warm in the cave. Let's wash our feet first and rest by the poolside - treat it as a hot sauna!"
Shen Bing nodded, "It's the only way for now."