The walk back up the bank does, in fact, noticeably suck. Merrin is taking a lot of breaks. In fact, by the time she's back at her cave, it's almost four hours since she left it and the temperature is up to 24° C. 

...Looks like it's about noon. She'll take another sun-angle measurement and then FLOP in her nice cool refreshing cave.

...Aaaaaand then she wakes up almost five hours later, which is possibly an indication that her almost-four-hour hike was pushing it too hard. 

It's midafternoon. Probably still nine or ten hours to go until sunset. 

She's getting great solar production! It peaked at 106 W and a bit of quick math and extrapolation suggests she's on track to be up, like, twenty percent from yesterday's yield – at least 1100 Wh, unless cloud cover shows up from nowhere. And she started out with 2150 Wh banked. She should be able to fully charge her suit tonight, refill her O2 tank all the way, and still have some left over in her main battery. 

...She should be able to do that even if she goes off and uses some suit power and oxygen doing a bit of Danger Cave exploration.

The question is just whether she's missed her safe window by having such a long nap. 

...There's no sign of the moon, so it set before she woke up. Low tide is past. 

Her model predicts that low tide should have been sometime between 30 minutes and 2 hours ago. And the tidal bore is six or seven hours after low tide. So even in the pessimistic case, she should have four hours, and it should be possible to do a suited-up cave trip and get there and back in less than three. 

Doooooooes she feel like betting that hard on the accuracy of her tidal model? 

...Even in the worst case, she probably still doesn't literally die? She might have to climb the opposite bank, and be stuck on the wrong side of the river until she can swim across, and then probably get swept around a bit by the current and have a long walk back to camp, at which point her suit would be getting low on charge and air, and she would have to reschedule tonight's excursion. 

But that probably won't happen. She's pretty sure that she has four hours at minimum, and that she can avoid getting lost in a cave and will be back within three. 

And she's under time pressure. Her food situation is actually pretty dire. 

...She'll take the risk. 

She's getting fitter, or better at navigating the gravity and the terrain, or something. Fifty-two minutes and she's at the entrance to the Danger Cave. 

....It should perhaps have been completely predictable that a regularly flooded tidal cave would be really, really slimy. 

Merrin's boots have a lot of traction, aided by her extra weight in this gravity, and if she falls down, well, she is armored. She'll go a little further in. Carefully, and keeping a close eye on the time. 

That sure is a giant pileup of what looks like organic debris - strapwrack fronds are recognizable, some of the rest is impossible to identify without having seen the intact plant - and there sure does seem to be a bunch of stuff growing on it. Merrin is pretty glad right now that she can't smell the air when it's filtered before it reaches her nose. 

....Hmmmmm. She's going to try something. 

WHOOOOOOA BIOLUMINESCENT ALGAE!!!!!!

...And...worms...? Neat! 

Not the time to look in detail. She's been in here for twenty minutes, and should assume it'll also take twenty minutes to get back, which means she can afford, like, five more minutes further in... 

A sheltered cave tidepool! 

She's been around two bends, adding up to an acute angle - right now the passage is probably pointed approximately towards the sea, whereas the entrance was angled away from the incoming water. The cave obviously still floods, the water in the tidepool will be replaced twice a day, and she actually just went down a slight slope so it should be flooded even by neap tides, but the forces of the tidal bore will be significantly mediated. And it sure looks like some sort of rain drainage coming from the weird upward branch has, over time, eroded out a basin with a nice little lip. If she were, for example, to make a strapwrack-and-paracord cage and weight it with rocks, she could probably put live-catch sea life in there, and expect it to still be around when she returned days later...

Also: there's an alarm going off on her suit. Merrin might want to pay attention to that alarm. 

SHIT

THAT'S THE ALARM FOR PRESENCE OF RADIOACTIVITY

Merrin does not stick around to pull up the analytics and see exactly how radioactive the cave is. She books it out of there as fast as she (safely, cautiously) can, and she heads straight to the river, and she spends five minutes swimming vigorously against the current, to make sure that any radioactive goop that might have been adhering to the suit is thoroughly washed away. 

Then her sensors will no longer be detecting the presence of radioactivity near her!

Okay. It's okay. The alarm was for the external sensors; there's a separate sensor suite inside the suit, for tracking cumulative effective exposure, and again, she's going to pull up the analytics for it once she's safely out of the river channel, but the alarm didn't actually go off. Depending on what dose (that mostly didn't reach her) the external sensors picked up on, it might in fact still be safe to use the convenient tidepool for storage, if she hurries in and out. 

...She's going to harvest some more strapwrack while she's down here. She still has an hour and twenty minutes left before her still-very-conservative three-hour deadline, and she has ideas for building projects. 

SERIOUSLY though what is WITH this planet that wants to KILL HER! The cave was already a danger cave! Why did it also need to be RADIOACTIVE???

Fifteen minutes is long enough to find, like, a dozen distinct strapwrack plants, in order to carefully harvest a few fronds from each, carefully avoiding taking more than 20% of the total fronds on a given plant. She doesn't want to completely depopulate the strapwrack in her local tidal zone and cause some kind of downstream ecological problem.

That still gets her 27 total fronds, and she looked for particularly long intact ones; they're all at least 3.5 meters, and some might be as long as 4.5. 

She bundles them up with a length of paracord from her front pouch, and hurries back up the bank. 

Her timing was definitely conservative! She made the trip in two hours and 53 minutes, dawn was a little over 21 hours ago, and the ocean is still barely in sight. 

Outside temperature is slowly dropping, down to 25° C. Her cave is a lovely 14° C. Her solar panels are still getting a pretty good hourly wattage. 

Merrin has remembered her takeaway from the last time. She carefully coils up each strapwrack frond in a size and shape that will fit in her tub for later rehydration, and leaves them in front of the tent in piles; they'll freeze-dry overnight, and this way they'll stay a bit out of the wind. 

Time to get out of the suit, charge it fully, make some more oxygen, and see how much she has left in her main battery at sunset!